Dimension stone quarrying in ACP countries

The aim of this publication is to give a general overview of issues related to Dimension Stone exploitation. It will assist those people wishing to enter the stone business to gain a better understanding of the features of this sector at international level and of the steps necessary to develop a new project. For those already involved in the sector, it will act as a reference guide. The guide is divided in five parts. Part 1 gives a general background of the global stone market and the status of the sector in ACP countries. Part 2 presents an overview of the application of stone and the main terms and standards in use. In addition, some more in-depth data are given, as regards the geological approach to the study of deposits and the materials they contain. In fact, the analysis of the origin and evolution of rocks provides an explanation as to why stone materials are subject to a wide range of variations and, at the same time, helps to foresee such variations. In Part 3 follows an analysis of the main quarrying methods and technologies used. The phases necessary to develop a dimension stone project, from general survey to final feasibility are analysed in Part 4. Part 5 contains useful information for those wishing to become involved in this sector (references, list of laboratories for testing dimension stone and examples of cost estimates for marble and granite quarries). The work covers a wide range of topics and obviously does not claim to be exhaustive on each one. The reader is welcome to comment upon the topics of interest so that these may be examined more closely in future works.

Editorial Committee: Centre for the Development of Enterprise Vaflahi Meité (CDE mining sector Co-ordinator) Jan Baeyens (associate consultant) Authors:

Giulio Milazzo (business expert, Italy) Paola Blasi (IMM Carrara S.p.A., Italy)

Contributions:

Marco Cosi (CDE associated expert, Italy) Silvana Napoli (IMM Carrara S.p.A., Italy) Marcantonio Ragone (IMM Carrara S.p.A., Italy)

The authors wish also to mention the other experts in charge of the theoretical sessions during the training seminar organised by CDE, ICE and IMM in Italy in June 2000: Frederick Bradley (consultant), Piero Primavori (consultant) and Giacomo Porro (consultant). The kind assistance of Laura Fossati (consultant) and Piero Primavori (consultant) is acknowledged. The Internazionale Marmi e Macchine Carrara S.p.A. was contracted by the Centre for the Development of Enterprises to prepare this guide. ©2003: CDE – Brussels Printer:

Pacini Editore SpA Via A. Gherardesca, 56121 Ospedaletto (Pisa)

Distribution:This publication can only be sold only by the CDE and its official distributors. Price: € 60

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Contents

PART I Overview of the sector 1. INTERNATIONAL STONE SECTOR (SILVANA NAPOLI – IMM) ....................................................11 1.1 Recent history....................................................................................................................13 1.2 Current situation ..............................................................................................................14 1.3 Key-factors for entering the world market ......................................................................15

2. STATUS OF THE DIMENSION STONE SECTOR IN ACP COUNTRIES (MARCO COSI – CONSULTANT)..................................................................................................16 2.1 Caribbean ..........................................................................................................................17 2.2 Pacific ................................................................................................................................17 2.3 Sub-Saharan Africa ..........................................................................................................17 2.3.1 Eastern Africa ..........................................................................................................18 2.3.2 Central Africa – UDEAC area..................................................................................19 2.3.3 Western Africa – ECOWAS area ............................................................................19 2.3.4 Southern Africa – SADC area ................................................................................22 2.4 Analysis of distribution channels ....................................................................................28 2.5 Local, regional and international markets ....................................................................30

PART II Understanding the stone industry 3. TRENDS IN THE USE OF DIMENSION STONE (MARCANTONIO RAGONE – IMM) ......................31 4. TERMINOLOGY AND STANDARDS ................................................................................................34 4.1 4.2 4.3 4.4

Geological classification ..................................................................................................34 Commercial classification ................................................................................................35 Reconstructed stone ........................................................................................................37 Specifications, tests and analyses ..................................................................................37 4.4.1 Physical-mechanical tests ......................................................................................38 4.4.2 Petrographic and chemical analyses ....................................................................43

5. GEOLOGICAL DESCRIPTION OF THE DIMENSION STONE DEPOSITS ............................................44 5.1 Carbonate rock deposits ..................................................................................................45 5.1.1 Sedimentary carbonate deposits ..........................................................................45 5.1.2 Marble deposits ......................................................................................................53 5.2 Granite deposits ................................................................................................................57 5.3 Other dimension stone deposits ....................................................................................62 5.4 Location of the dimension stone deposits ....................................................................64 3

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PART III Quarrying methods and technologies 6. DIMENSION STONE QUARRYING ..................................................67 6.1 Quarry products ..................................................................67 6.2 Quarrying configuration ....................................................68 6.3 Quarrying sequence............................................................72 6.3.1 Pre-production operations ......................................73 6.3.2 Primary cuts ..............................................................74 6.3.3 Secondary cuts and removal of blocks ..................74 6.4 Quarrying technologies......................................................74 6.4.1 Cutting by drilling ....................................................75 6.4.1.1 Drilling equipment ......................................80 6.4.1.2 Wedging ........................................................83 6.4.2 Cutting by abrasion ..................................................83 6.4.2.1 Helicoidal wire saw ......................................84 6.4.2.2 Diamond wire saw ........................................85 6.4.2.3 Chain saw ......................................................86 6.4.2.4 Diamond belt saw ........................................86 6.4.2.5 Disk cutter ....................................................93 6.4.3 Cutting by disaggregation ......................................93 6.4.3.1 Flame jet........................................................93 6.4.3.2 Water jet ........................................................95 6.4.4 Overturning of benches ..........................................97 6.5 Handling and transport of blocks ....................................98 6.6 Selection of quarrying technologies ................................98 6.7 Professional skills ............................................................102 6.8 Quarry safety and security ..............................................104

PART IV The project cycle 7. PRE-INVESTMENT STUDIES ........................................................107 7.1 7.2 7.3 7.4

Survey ................................................................................108 Exploration........................................................................110 Preliminary market study ................................................113 Quarry planning ................................................................113 7.4.1 Quarry design..........................................................114 7.4.2 Quarry operations ..................................................115 7.5 Environmental impact study ..........................................116 7.6 Feasibility study................................................................120 7.7 Quarry optimisation ........................................................122

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Contents

PART V Annexes Annex 1

References ....................................................................127

Annex 2

List of Laboratories for Testing Dimension Stones ..129

Annex 3

List of Equipment for a Marble Quarry (2,000 m3/yr of sized blocks) including spare parts and consumables for a 12-month operation ..137

Annex 4

Example of Cost Estimate for a Marble Quarry (2,000 m3/yr) ..................................................................141

Annex 5

List of Equipment for a Granite Quarry (2,000 m3/yr of sized blocks) including spare parts and consumables for a 12-month operation ............145

Annex 6

Example of Cost Estimate for a Granite Quarry (2,000 m3/yr) ..................................................................149

Annex 7

List of Equipment for a Marble Quarry (4,000 m3/yr of sized blocks) including spare parts and consumables for a 12-month operation ............153

Annex 8

Example of Cost Estimate for a Marble Quarry (4,000 m3/yr) ......................................................................157

Annex 9

List of Equipment for a Granite Quarry (4,000 m3/yr of sized blocks) including spare parts and consumables for a 12-month operation ............161

Annex 10 Example of Cost Estimate for a Granite Quarry (4,000 m3/yr) ..................................................................165 Annex 11 The naturally cleft stones (NCS) (Marco Cosi – consultant) ..................................................169

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Preface

There is huge potential for the stone industry in ACP countries as a result of the presence of a large number of deposits with high quality raw materials and the development of companies with the partial support of national and international institutions. Moreover, the industry is a traditional industry in the ACP countries based on a productive model of small- and medium-sized companies with low capital entrance barriers and high labour requirements, thus an industry which can create new employment. This, however, is obviously not enough to ensure development. Much has already been done in the right direction and the achievements so far rightly lead companies and institutions alike, fully committed to their development plans, to foresee a bright future for the industry. The CDE has invested substantial time and resources with a view to improving the competitive edge of stone companies working in the ACP countries. This it has done with expertise and above all with the accurate selection of projects to be carried through to execution since this is the only way to guarantee positive results. Hence, this guide is not an isolated piece of work but the result of long-term programmes and plans of action. The Associations AFRISTONE and ADOPIEDRA, created thanks to the resolve of the companies and the support of the CDE, believe the guide to be a very important tool for the industry in ACP countries since it contains valuable information, suggestions and tips specific to the quarries and working conditions in these countries. The guide is also an excellent example of a successful joint effort on behalf of the companies. The content of the guide reflects the thorough work of a competent, professional group of experts with the full collaboration of companies and entrepreneurs in the ACP countries who freely gave exclusive information, data and suggestions. The associations AFRISTONE and ADOPIEDRA who encouraged the support by the stone companies in the ACP countries for the publication, are satisfied in achieving one of the main objectives of a true association.

ADOPIEDRA Mr. Manuel Reyna Chairman

AFRISTONE Mr. Fazie Baksmaty Chairman

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Introduction

This guide originates from the need to answer the clear and welldefined questions asked by those operators whose activities are carried out in the 78 member countries of the Cotonou Partnership Agreement, generally referred to as ACP (Africa, Caribbean and Pacific) countries. Such a varied topic as stone quarrying cannot actually be addressed through general rules or relying on the imitation of successful models. A reflection on the actual scenario of ACP infrastructures is enough to understand that there can be no comparison to any other situation. In these countries, actions need instead to be planned based on the peculiarities of the companies and all that surrounds them, and accept for instance that production problems can be more effectively solved using proven technology rather than latestgeneration machinery. Here more than elsewhere, when a business can have a future if it can successfully planned and organised, the method selected becomes decisive for the final result. Aware of these facts, CDE has been for years supplying efforts and resources to the stone sector in ACP countries, and has successfully completed a large number of projects and assisted numerous businessmen to overcome problems which prevented their companies from growing and to improve their production standards. In particular, the EU and the CDE have implemented some sound policies to assist the private sector in this development, also through participation in: Industrial Mining Fora: 1994 Lusaka, organized by SADC-MCU Secretariat, EC and CDE 1998 Accra, organized by ECOWAS, UDEAC Secretariat, EC and CDE 2000 Lusaka, organized by SADC-MCU Secretariat, EC and CDE Technical and Commercial Missions: 1997 Ethiopia-Eritrea 1998 Namibia 1999 Dominican Republic 2001 Madagascar 2003 Dominican Republic

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Introduction

Training Workshops and Courses: 1996 Borba – Portugal 1999 Dublin – Ireland 2000 Carrara and Sardinia – Italy 2003 Carrara – Italy International Fairs: 1995 Carrara – Italy 1997 Madrid – Spain 1999 Düsseldorf – Germany 2001 Nürnberg – Germany 2001 Carrara – Italy 2003 Carrara – Italy An intense action resulting in important issues: ACP countries possess large deposits of attractive ornamental stone, widely presented in technical publications (see references 19 and 20 in Annex 1) and highly appreciated in the stone world; improvement is needed in order to be more competitive in the international market filling the gaps related to the production cycles, the work organization and the market knowledge. Programs and actions have been developed consistently with the actual information and the goals to be achieved have always been suited to the companies’ potentials, as it should be; from the very first projects, through partnerships, to the implementation of production activities through to market relationships. More than 80 ACP Dimension Stone projects have been and are still assisted by CDE in the last 6 years, by co-financing part of the technicalmarketing and training pre-investment expenses. These actions undoubtedly and substantially helped to develop the DS sector in the ACP area. But, if it is hard to enter a market, it is even harder to stay there, and competition has to be faced using suitable means; labour’s professional skills are among the most important factors to resist and progress in this sector. At this regard one of the most important tasks for the CDE is to ameliorate the competitiveness of the ACP stone materials and products. Hence the effort which CDE has decided to put into training and specialisation activities for quarry operators; geologists, technicians, quarry foremen or quarry labour have, therefore, been selected for a 20 days’ training period in Italy through theoretical sessions and hands-on experience, really close to working problems and situations. The results have been satisfactory for all the people involved, and the program for improving the ACP stone industry is still under progress. In fact the present guide is the second step, after the training seminar, of the whole program to enhance the ACP stone industry; it collects and widens the lessons learnt by the trainees and makes them available to those who have not had this opportunity yet. 10

PART 1

Overview of the sector

1. International stone sector The international stone industry plays a primary role in the building market and in the field of finishing materials for the building industry. The application of dimension stone in floorings and claddings in general or in urban landscaping is certainly the most common one, both due to the amounts of materials used and to the overall turnover involved. Another important application is funerary art and monuments in general, both for marble and granite and other special stones, which are generally local or belong to the tradition of use. Urban landscaping, objects d’art, artistic sculptures and reproductions are minor applications, even if these market niches are very often prestigious and with high added value (e.g. contemporary stone sculpture of Zimbabwe, appreciated in Europe, America and Australia). Once stone has come out of a quarry, it has to undergo different processes and market distribution networks. These networks are differentiated as follows: • raw materials, mainly squared blocks, but also shapeless blocks and rock pieces; • half-finished products: polished and non-polished slabs, cubic stones for block-cutters, raw tiles, etc.; • finished products: special finishing, polished marble, decorative items, sculptures, objets d’art, funerary products, etc. These circuits often intermix, especially for finished and semi-finished products, though their distinguishing features do not change, but mainly adapt to each outlet market. There are some features which are shared by the whole sector, and some historical processes, in particular, which have deeply affected the last twenty years. They have brought the ascertained world-wide production from approximately twenty million tons of quarried materials in the early eighties to over sixty million tons today (see Table 1). This process of growth is still far from getting to an end. These factors have been linked to international events, which had nothing to do with the stone sector, but which have ended up by associating it to other expansion trends, sometimes in a way which deeply differs from that of other internationally-traded raw materials. 11

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Table 1. International production of raw materials (metric tons). COUNTRIES ARGENTINA* AUSTRALIA * AUSTRIA* BRAZIL CANADA * CHINA CZECH REPUBLIC DENMARK EGYPT FINLAND FRANCE GREECE INDIA * IRAN * ISRAEL ITALY JAPAN KAZAKISTAN MEXICO NORWAY POLAND PORTUGAL ROMANIA SAUDI ARABIA SOUTH AFRICA SPAIN SWEDEN TURKEY USA UZBEKISTAN TOTAL

1997

1998

1999

2000

2001

214.200 28.069 300.875 2.114.000 320.989 12.960.000 364.724 nd/na 120.000 238.106 1.197.650 2.100.000 8.172.000 nd/na 71.000 9.712.809 234.000 307.530 516.805 181.278 nd/na 1.200.000 nd/na 600.000 891.172 5.292.000 95.350 2.000.000 1.180.000 117.033 50.412.557

231.115 37.566 415.115 2.181.753 356.000 13.000.000 297.400 8.075 120.000 278.627 1.100.000 2.000.000 8.572.000 6.500.000 70.000 9.427.831 212.568 381.780 664.000 164.186 nd/na 1.877.524 59.570 600.000 960.780 5.557.000 90.500 2.400.000 1.130.000 89.460 58.693.390

226.993 40.000 376.430 2.200.000 332.800 13.000.000 250.000 21.127 150.000 293.128 1.300.000 2.000.000 8.760.000 7.045.000 80.000 9.756.635 207.577 328.860 744.376 262.000 232.050 1.899.644 61.523 600.000 1.000.000 5.600.000 105.762 2.304.000 1.250.000 78.336 60.427.905

220.300 40.000 528.034 2.400.000 350.000 13.000.000 300.000 21.000 150.000 300.000 1.300.000 2.000.000 10.054.000 7.413.451 80.000 10.129.673 160.500 300.000 1.034.529 242.000 259.100 1.900.000 83.154 580.000 1.000.000 6.200.000 100.000 2.453.000 1.250.000 79.566 63.848.741

280.000 31.180 500.000 2.500.000 300.000 16.800.000 300.000 21.000 150.000 350.000 1.500.000 2.000.000 10.100.000 7.536.000 80.000 10.463.900 150.000 225.300 1.000.000 224.000 274.100 2.000.000 90.000 600.000 1.000.000 6.200.000 100.000 2.625.000 1.300.000 80.000 68.700.480

Sources: Local Official Institutes or Associations - IMM elaboration *: 1. Data in italics are estimated. 2. Countries with unreliable sources over two years have been omitted. 3. Limitations/Sources – Australia: ProdCom data. – Australia: only marble, granite and basalt productions have been considered. – Canada: sandstones have not been included. – China: this figure is a mean value between the Associations’ figure and data from other sources. – Czech Republic: 1997 and 1998 data include smaller-sized granite. – Denmark: ProdCom data. – Egypt: 1997: ’96-’97; 1998: ’97-’98; 1999: ’98-’99; 2000: ’99-2000; 2001: 2000-01. – India: only marble, and granite productions have been considered; 1997: ’96-’97; 1998: ’97-’98; 1999: ’98-’99; 2000: ’99-2000; 2001: 2000-01. – Iran: 1995: ’94-’95; 1996: ’95-’96; 1997: ’96-’97; 1998: ’97-’98; 1999: ’98-’99; 2000: ’99-2000; 2001: 2000-01.

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1.1 Recent history The quarrying and processing of marble are activities which take root in the remote history of many civilisations, from which it inherited and still preserves a high-profile, almost sacred image, which is reflected in the products and to some extent in the users. Along with the availability of the materials, which has enormously grown and spread, this image turns stone into a status symbol, and, at the same time, into a daily, confidential object, sought after and longed for, and more or less used on all markets, at all latitudes. Its use is dictated by and depends on local traditions, the economical and cultural features of each area, current fashions, sometimes on the climate. It nevertheless always remains an echo from the past, as is repeated by any advertising agent who wants to set up a campaign for this material. In the early eighties, the range of countries which produced raw materials was already remarkably larger than in the early fifties, and some processes, which would then expand and affect the sector through to the end of the century, were already under way. 1984 was the benchmark by the powerful entrance of granite into the production scenario, and by the strong incidence of international types of contracts, based on major works on the one side, and European and Middle-Eastern consumption on the other. The main producer countries were actually European, first and foremost Italy, but also Spain and Portugal, both for marble and granite, and Greece, France, the Scandinavian countries, Belgium, the Soviet Union and Yugoslavia. Then Brazil, India, South-Africa for granite, and Iran joined the group, while Turkey was beginning to show up, and along with it a series of minor producers, which was bound to slowly grow to the point of becoming the over forty significant countries of today. In those times, the main consumers were the United States, Germany, Italy and few other European countries, Japan and the Arabian countries in general. At different levels and often with different average values per ton of consumed product, some South-American and North-African countries, as well as the Far East, with Hong Kong and Singapore, and some other countries, attracted also the attention of major international producers. The striking aspect of those years was the use of granite in buildings with a strong vertical development, and marble in Middle Eastern countries and hot countries in general in strongly customised applications, through important contracts, involving the extremely highlevel architects’ practices and both the international general contractors and stone companies, especially from Italy, able to manage a contract from the beginning to the end, and at levels of extremely high specialisation and complexity. Along with this profile, mass-produced materials were also used in markets which were, however, equally sig13

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nificant, such as Germany. The market of restoration and maintenance of buildings was progressing all over Europe, and European Community in particular; less was built, but more was restored. Existing buildings were improved and altered. Market consumption in general was quickly speeding up, while the trend to set out in search of new materials, new colours and new colour textures, was getting stronger. The threshold which new producers had to overcome to access this industry was comparatively low, and the search for new materials to be launched on the market was highlighted and intensified. This was also supported by the political decisions taken by some major boards, which supported the development of third countries, identifying the stone sector as a sector which needed to be supported and developed in many areas. The range of producers of raw materials was thus quickly widening, involving some changes to the classical model, which have deeply altered the general scenario up to these days. In addition, a general process, involving marble and stones as well as many other resources, had just lately begun: a general trend to shorten the distribution chains, leading to a growing regionalisation of trade and traffics. Stones are, moreover, a heavy good, expensive to transport, and so, whenever possible, one tries to meet the market’s demand with local productions. These are also found to be culturally closer to the consumer market, since they relate more to specific traditional uses. Each country and each area has its own stones, historically used in local architecture: in this period, they were rediscovered and promoted again in an updated manner, placing them alongside new stones, which were discovered and launched on the trade network since the very beginning.

1.2 Current situation At this stage, the above processes have given shape to two trading levels of raw materials: • one for more prestigious stones, those with special technical or aesthetic features, the value of which is recognised world-wide; • one for those stones which have common features which makes them more suitable to meet the demand of a minor regional market. Similar considerations apply to finished products, since some classes of products obviously do not reach the finishing and specialisation level required for a high-profile network. They are consumed locally or on near-by markets, since the overload resulting from the transport costs required to move them to different areas would make them loose their competitiveness. Obviously, there are further variations and intricacies on local markets too. Primarily there is a division by growing consumer ranges 14

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along with the recent trend to meet the local demand through selfsufficient productions. Such are the main characteristics at the beginning of the new millennium which have even led to the successful opening of completely new markets. The recent development of new productive scenarios for raw materials has led to significant alterations in the international stone industry in general. These alterations have in turn become the propelling force for other new processes, triggering off other upheavals. The overall result is a powerful increase in the amounts of quarried, sold and used materials, and in the number of producer countries from just about twelve to over forty.

1.3 Key-factors for entering into the world market The following factors are strategic for the basic development of a stone production pole, starting with the quarry: 1. possession of raw materials, with the following characteristics: • constant aesthetic features; • available in quantity and quality (technical and aesthetic) sufficient for the end use; • possibility of obtaining blocks of commercial size and shape. 2. accessibility to deposits implying adequate transport facilities. 3. possibility to comply with supply times. 4. closeness to the market. 5. control of exclusive rights, or admission to reliable trading networks. 6. knowledge of the competitors. 7. technical and marketing know-how. As far as the integration of a production cycle is concerned, there are some examples of productive poles, specialised only in the processing of materials, with no direct privileged access to at least one kind of stone. These examples result from quite atypical historical processes, originated in any case from local stones, the exploitation of which must have been quitted or worked out later. The classical process of birth of a stone production pole always starts from a quarry or deposit. And this, instead, accounts for the value which the possession of a raw material entails for the process of economic development of a sector. Nevertheless, especially at the beginning, production cannot be easily organised in a vertical system, by combining mere quarrying to more or less complete forms of processing. Historically, the cycle integration process has always evolved by stages, sometimes fast, but only where there were previous historical conditions of practice with the stone, which the new quarrying and exploiting technologies have only allowed to rediscover. In other words, it must be borne in mind that modern processing technologies may make 15

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things much easier, but do not replace man or man’s knowledge, which cannot always be fully codified. What role does a domestic market play? It plays a decisive role in the success of a stone industry, but it does not have to be purely domestic. It just needs to be close, in the vicinity, physically and commercially easy to reach: a simple and reliable outlet reservoir. To have such a reservoir available means to be able to rely on a propelling force, which helps overcome the market’s dead times, which can always happen, for any stone. In addition, it is an irreplaceable training ground for all the altering stages of the productive and commercial cycles which a stone experiences during its life cycle. What role does the international market play instead? The international success of a stone stems from a set of factors which substantially depend on the features of the stone itself and its regular availability in the market; and then on the ability to fit in a trade network which may bring it to its proper end-level of promotion. Sometimes, the success of a material depends on indirect channels, such as its application in prestigious works of architecture, subsequent to its selection by a famous architect. Or sometimes new materials even go through an application, as substitutes of better known, more soughtafter and more expensive materials, which they resemble or remind of for some special features. There are some recent examples of this in the world, though they often show that attention must always remain alert, because styles go out of fashion and markets change, and it takes a long time to stabilise a production in terms of durability.

2. Status of the dimension stone sector in ACP countries In ACP countries and Caribbean and African ones in particular, the Dimension Stone (DS) Sector has been remarkably active for the last 1520 years and 5-10 years, respectively. In the Caribbean Islands, particularly in the Dominican Republic, the sector is very active and well organised. Several private entrepreneurs have invested a lot in quarrying and processing projects (mainly marble and coral limestone). A large trade of finished products currently exists between the Caribbean countries on one side, and the USA and Spain on the other. In spite of the great difficulties due to socio-political and logistic-infrastructural conditions, several African private companies have started new DS projects, mainly in the quarrying, as a result of the incredible un16

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exploited and un-evaluated geological potential of the continent (see Figure 1). Unlike South Africa, Zimbabwe and the Dominican Republic, where the DS sector has been active for more than 20 years, the development of the DS sector in other ACP countries has been partly due to private initiatives and partly to EU and International Institutions (see EU, CDE, World Bank, Sysmin, UNIDO, IFC and other international financial institutions). The situation of the DS sector in ACP countries can be presented as follows.

Figure 1 DS CDE Projects in ACP African Countries (by M. Cosi).

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2.1 Caribbean As already mentioned, the Dominican Republic, with its limestone/marble quarries (portoro-like marble, coral limestone, botticino-like limestone etc.) and more than 10 processing plants of different sizes, is of major importance: at least 20 private quarrying, processing and trading companies presently exist mostly oriented to the USA and Spanish market. In the last 5 years some European companies have also signed commercial-technical partnership agreements with local companies. A review of the Dominican Republic potential is contained in the CDE Guide “Dimension Stone Sector in Dominican Republic”, published in 2000. Other potential Caribbean countries are Jamaica, Haiti (limestone and marble), Suriname (black and red granites). Cuba, although not officially belonging to the ACP group, will probably become the future DS pole in the area, with its huge marble and limestone potential and medium/high technical-marketing skills. The majority of the overall production of finished dimension stone from the Caribbean is exported to the U.S.A. (mainly Florida) and Spain. More than 80 % of raw blocks are processed locally. The rest is mainly exported to Spain and to the USA to a limited extent.

2.2 Pacific In the Pacific, the DS sector is very limited, although with interesting geological potential. The coral limestone quarry operations in Fiji and the huge geological potential of Papua New Guinea are undeveloped for lack of infrastructure and transport facilities and due to the long distance to the main markets.

2.3 Sub-Saharan Africa This is certainly the most important and potentially most significant ACP area in terms of DS. Sub-Saharan countries, like Ghana, Nigeria, Benin, Senegal and Mauritania in Western Africa, Sudan, Ethiopia and Eritrea in Central-Eastern Africa, and all SADC countries, are certainly attractive for many EU companies, with their high-quality and peculiar materials, such as blue, yellow, black, dark red and other unusual “new” granites and white and pink marble. Although several DS quarries of different sizes are operational in these countries, very few processing plants exist with examples in South Africa (25-30), Zimbabwe (8-10), Namibia (2), Nigeria (4), 18

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Ethiopia (4-5). Other modern plants operate in Ghana (1), Eritrea (1), Madagascar (1), Angola (1-2), Mozambique (1), Zambia (2), Sudan (3). A more detailed overview of the current DS status in ACP African countries, divided by area and by country, is provided below. 2.3.1 Eastern Africa (Eritrea, Ethiopia, Sudan, Kenya, Uganda) This area is mainly characterised by a vast outcropping of mainly unexplored granites and gneiss-migmatite rocks and, to a more limited extent, old and very young marble. They are often intensively fractured, due to the geo-structural location of the area, across the southern branch (rift) of the “triple point” of the Red Sea. They sometimes present encouraging DS features: large, non-fractured outcropping areas (see Tigrai), grain homogeneity, grey, pink and red colours and un-weathered outcrops. The old metamorphic basement outcropping in Central and Northern Ethiopia (Tigrai), Eritrea and central-eastern Sudan is particularly interesting. Marble is also outcropping within the basement, in deformed and folded bands and lenses. Attractive black, pink and white marble has already been discovered in Eritrea, Tigrai and central Sudan. Marble and beige limestone are also quarried in the Harar region of Photo 1. A quarry of coralline stone in Dominican Republic Southeast Ethiopia and in (by M. Cosi). the Southwest area, close to the Sudanese border. Finally, interesting porphyry meta-volcanic rocks (red and green) and some red travertine exist in Northern Ethiopia, which could represent an important potential for the “porfido” market. In Ethiopia, the local DS sector is well-developed and at least six companies are presently operating; two of them have signed agreePhoto 2. Jamaica: a travertine quarry (by P. Primavori). 19

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ments with European operators in the last few years. Several small-size marble, limestone and granite quarries are in operation in the Harar region and close to the Sudan border in South and Southwest Ethiopia and in the northern Tigrai region. Three processing plants (two of which are very large and modern) and some smallsize plants (mainly artisanal workshops) are working in both countries. In Sudan and Kenya some successful marble projects exist, although not very developed, mainly due to lack of infrastructure and contacts with Western markets (Sudan). Sudan has a great potential for granites and mainly for marble (rosewood type, white, pink and grey). The local DS sector is certainly one of the most dynamic and potentially the most significant one in the area, with its many private quarrying and processing companies. This area is very well located with respect to the potential markets, being very close to the Arabian and Middle Eastern countries, the SADC area and having its main ports situated along the main routes to the EU and the Far East. Unfortunately, these countries are not yet competitive and ready to approach the international market: quality and consistent production are key-issues. Important potential markets are Saudi Arabia, U.A.R., Egypt, USA, the Middle East and the local markets. The main Ports in the area are: Massawa (Eritrea), Assab (Eritrea), Port Sudan (Sudan), Mombasa (Kenya) and Djibouti. 2.3.2 Central Africa – UDEAC area (Congo Brazzaville, Gabon, Central African Republic, Cameroon, Equatorial Guinea) Due to the presence of the Congo craton and the related metamorphic mobile belts, and in spite of the total lack of information and exploration campaigns, this area has probably the greatest unexplored potential in Africa. The lack of infrastructure and know how, and the climate make it very difficult for these countries to be explored and correctly evaluated. At present no significant DS activity exists in the area, except for imports of finished products and very small artisanal workshops in Cameroon. The main ports in the area are: Point Noire (Congo), Libreville (Gabon) and Douala (Cameroon). 2.3.3 Western Africa – ECOWAS Area (Mauritania, Senegal, Cape Verde, Guinea, Ghana, Togo, Ivory Coast, Liberia, Sierra Leone, Benin, Nigeria, Mali, Niger, Burkina Faso, Chad) This area is undoubtedly very promising, “the last, but not least” from the point of view of the development of the dimension stone sector. 20

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Photo 3. Ethiopia: blocks of pink granite (by M. Cosi).

The DS sector is developed in three countries only: Ghana (four granite quarries, one modern processing plant and three DS operating companies), Nigeria (six granite quarries, three processing plants and six-seven operating companies) and Mauritania (several new granite/marble quarries). Countries as Togo, Ivory Coast, Benin could also become important granite producers over the next ten years. Granite productions of Nigeria and Ghana (mainly banded pink and light-grey granites/migmatites) are exploited since 1993-94 and mostly sold on local markets. Attractive marbles (Senegal) and granite (Benin) have been discovered in the last three years, and partnership agreements with EU companies are foreseen. A strong supporting factor for the implementation of the DS sector will surely be the existence of important, well-equipped ports, located close to the quarry sites: actually, Lagos in Nigeria, Douala in Cameroon, Accra in Ghana and Abidjan in Ivory Coast, are already famous international commercial harbours, and most international freight companies operate there.

Photo 4. Belfast Black quarry in RSA (by P. Primavori).

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Photo 5. Kenya: a blueish marble quarry (by M. Cosi).

Photo 6. Preliminary opening in grey granite quarry in Dourdeb area – Eastern Sudan (by P. Primavori).

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2.3.4 Southern Africa – SADC area (RSA, Zimbabwe, Namibia, Botswana, Malawi, Mozambique, Angola, Zambia, Tanzania, Democratic Republic of Congo, Lesotho, Swaziland) and Madagascar This area, covered by the two recent Mining Forums held in Lusaka (Zambia) in 1994 and 2000, is undoubtedly the most developed and the most important area in Africa for the DS sector. An extensive review of the SADC potential is given in reference 19 (Guidebook of DS potential in SADC region). South Africa and Zimbabwe together cover more than 70% of the total dimension stone production of Sub-Saharan Africa. Granites, marble and naturally cleft stones (quartzites and glitterstones) outcrop and are exploited in most SADC countries. Tanzania has a quite large potential, but preliminary studies did not identify any particularly interesting stones suitable for export to date, except travertine and onyx stones outcropping in the southern area. The local markets both in Tanzania and in Kenya are, however, strongly growing and this fact would surely help the development of the sector in this area.

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The main port, one of the largest in Africa and already utilised for the DS trading, is Dar Es Salaam. The territory of the Democratic Republic of Congo, although mostly covered by sedimentary and volcano-sedimentary sequences, also includes a large, totally unexplored area where highly potential metamorphicgranitic old Precambrian basement outcrops. At present no DS activities exist in the country, excluding a limited import of tiles from Italy. In Zambia, a famous blue granite is quarried in the Northwestern Province and exported all over the world by an Italian company which commenced operations in 1992. The same company opened a pink-green marble quarry very close to Lusaka in 1992, and restarted it in 2000 with the intention to supply the new modern tiles processing plant, currently being built in the Lusaka West area. Two smaller projects (quarrying and processing) for white, pink and dark grey marble are in operation, although only serving the local and regional markets. A great geological potential exists for red and pink syenites and granites in many areas of the country, and for dark, pink and white-pink banded marble around Lusaka and in other areas of central Zambia. Some other occurrences of blue granites exist in the North eastern Province, close to the Malawi border and close to Lusaka (currently undergoing evaluation and preliminary facing tests). Glitterstone outcropping areas are located in the Kariba District, in the Southern region of the country. In Malawi, some projects for exploiting particularly high-quality granite have been started over the last 3 years. A blue granite quarry, not yet fully operating, is located in the Northern region, close to the Tanzanian border. A very attractive green amazonite granite is quarried by a Joint Venture company (local and Italian) in the Rumphi area, 40 Km west of Msuzu. A good potential for marble, pink banded granites (garnet bearing migmatites) and black “granites”, similar to the famous Zimbabwe Black, also exists, respectively in central eastern and central western regions. In Mozambique, the potential is remarkable, although quarrying activities have suffered from the previous political instability and the present lack of infrastructure. Black granites, anorthosites, blue and brown-golden labradoritites, and several kinds of coloured migmatites and granites outcrop in the Northern and Western regions. Light marble is known in the Pemba area and in several neighbouring zones. Finally, a new interesting sub-outcropping area of blue dumortierite bearing quartzites, similar to Brazilian “Azul Macaubas”, was discovered some years ago, but it has not been totally assessed yet. 23

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Italian, Portuguese and Southafrican companies have started exploration campaigns over the last two years. The most important Ports are Maputo, Beira and Nacala. In Angola, Portuguese companies are operating in the south, producing black “granites” (labradoritites), in spite of its huge but undeveloped DS potential because of lack of infrastructure. Granites (pink, red, blue and black), migmatites, marble and quartzites outcrop in several areas (mainly in the South), with really good characteristics, to be assessed for future DS projects. The most important Ports are Lobito and Luanda. In Botswana, the older metamorphic basement outcrops only in the Eastern part of the country, while the rest is covered by the Kalahari formations. Apart from some orbitolitic Rapakivi-like granites outcropping South of Gaborone (called Manyana Granite), no particular interesting rock, suitable for overseas export, has been identified to date. Namibia is one of the most attractive countries for DS operators, both due to its considerable geological potential and its good investment climate and infrastructures. Many different types of old and younger granites and marble outcrop in the country, most totally unfractured and un-altered. Moreover, a certain potential for “porphyry” stones also exists Photo 7. Rustemburg granite quarry in South Africa (by P. in the central region. Blasi). A vast area of white, pink and rosewood-like marble is located in Central Namibia (Karibib region), where some quarry projects are already operating. Other interesting types of marble outcrop in the Northern region (white) and in the South (black). Yellow granites are presently being quarried, while many other potentially significant areas exist. Investors have in general good chances of becoming future leaders in the yellow granPhoto 8. Zimbabwe Black quarry (by IMM Archive). ite market. 24

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Moreover, red and pink migmatites and gneiss (multi-colour type) outcrop in the Swakopmund and Walvis Bay areas and in many other areas of central Namibia. A blue “granite” has been known for 20 years in the Northern Cunene region. In 2000, the project was re-started following the entry of new Italian and German partners. At present, only 2 important Italian DS companies are producing and exporting yellow granites and rosewood-like marble. Some SouthAfrican, Italian and Spanish companies are carrying out preliminary field explorations. Two processing plans, financed by Sysmin and the Namibian Minerals Development Fund, are operating in Karibib and Omaruru. Zimbabwe is known for “Zimbabwe Black Granite”, which is mainly quarried in the Mutoko, Murewa and Mount Darwin areas in the Northeastern province, although other new important projects have been started in the surrounding areas (Shamva, and Matawatawa). The average annual production of “Zimbabwe Black” amounts to 160,000 tons of raw blocks, 140,000 of which are exported to South Africa, Europe, Taiwan and Japan. The rest is finished locally, mainly in two major processing plants and other smaller workshops. The biggest quarries are generally well-equipped and the technical management has medium-high skills. Other quarried materials are a type of brown granite (Harare), a type of black granite similar to Indian “Black galaxy”, named “Stargate” (Mont Darwin), and a type of granite similar to Rustemburg granite, named “Magic black”. Potential materials, part of which have already been tested and preliminarily quarried, are green-marble in the central region (Kwe-Kwe) and coloured banded marble in the Eastern region (Nyamapanda area), near the Mozambican border. A strong potential certainly exists for some new findings of Zimbabwe Black and other types of granites and migmatites within the Kalahari craton. More than 15 companies are fully engaged in granite quarrying in Zimbabwe. Two large and five small-medium processing plants are operating, although only two are in the position to produce high-quality granite slabs to be exported overseas. The DS stone sector of the Republic of South Africa started in the early eighties, following the opening of the “Belfast Black granite” quarries in the northern region, producing one of the best absolute black granites which was intensively exported all over the world until the early nineties. Other famous South-African black and dark grey granites are Impala Black, Nero Africa and Rustemburg. They are exploited in a vast area Northwest of Pretoria and are intensively exported world-wide. These materials, very well established on the international markets, are gen25

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erally used to produce large tiles for big building projects, due to the large ore deposits available and their good colour and texture homogeneity. At present, the production of grey and black granites accounts for 87% of the total granite production in R.S.A. In addition, South-Africa produces other interesting granites, such as: – light Paarl granite (Cape Region); – African Juparana; – African Lilian pink granite (Eastern Transvaal); – African Red (Potgieterrus in Northern R.S.A.); – and other red granites; – Verde Fontaine; – Olive Green and other similar granites (Puff Adder area in the Northwestern part of the country). Finally, several attractive quartzites and sandstones are extracted in Namaqualand (Northwest region). RSA, has no important marble reserves, except for a banded whited grey-marble extracted North of Cape Town. South Africa and Zimbabwe with its “Zimbabwe Black” are undoubtedly the only African countries to be really known as producers and exporters of raw and processed DS. Many companies and mayor groups operate in these countries, most of them with several branches and Photo 9. Zambia: marble quarry near Lusaka (by P. Primavori). offices in the EU and worldwide. The main ports in the area are: Dar Es Salaam (Tanzania), Beira (Mozambique), Durban (RSA), Cape Town (RSA), Walvis Bay (Namibia), Lobito (Angola), Namibe (Angola). Madagascar (not included in SADC group) is unique both in geographical and geological terms. In fact, the large African island is geologically “part” of the Indian continent, from which it parted during the evoPhoto 10. Zimbabwe Black granite quarrying in Mutoko area – Block squaring (by M. Cosi). lution of the plate movements. 26

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The geological DS potential of this country is huge. Granites, migmatites, syenites, quartzites (even blue), blue labradorites and marble outcrop all over the country. However, the comparatively young structural events which have affected the island and the poor infrastructures often interfere with the development of new DS projects. Regional studies carried out by Italian and French compaPhoto 11. Large rose migmatite quarry in central Nigeria, nies have identified good DS Kaduna area (by M. Cosi). investment opportunities. At present, only a few quarries exist, opened in the middle 80’s, and currently not fully operating. They are run by local joint-venture company established by important Italian and South-African DS companies. New exploration and quarry start-up operations are currently carried out by the above companies. Only one granite modern processing plant is operating in the country, in the town of Photo 12. Blue syenite quarry in Mauritania (by M. Cosi). Ambatofinandrahana. The main ports in the country are: Toamasina, Toliara, Morondava and Majunga. From a market point of view, this area, mainly formed by the SADC countries, is undoubtedly the most developed and advanced one, also in terms of marketing. Several countries are historically important exporters of raw black stones, such as: South Africa (Belfast Black, Rustemburg, Nero Africa, Impala, African Red, Verde Fontaine, Olive Green and other new types of granites), Zimbabwe (mainly Zimbabwe black), Namibia (White, Pink and rosewood-like marble), Zambia (Blue granite and some banded marble) and, to a limited extent, Angola (Black labradorites, mainly exported to Portugal). In the last few years, some of these countries (South Africa and Zimbabwe) have also started to export finished products, mainly to USA and Japan. 27

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A second group of countries is trying to approach the international market with new attractive and peculiar materials: Malawi (blue and green granites), Madagascar (blue quartzites), Mozambique. The South-African area is certainly one of the most active and potentially significant ones in the entire international DS scenario.

2.4 Analysis of distribution channels The dimension stone sector is unique and critical from a marketing point of view, mainly because very few people exactly know the real properties of a stone, and the largest market share is in the hands, firstly, of importers, and secondly, of architects. Moreover, unlike other quarrying sectors, the quarrying of a block is only the beginning of the trading path. If we extract one kilogram of gold or one ton of gravel, we already know their value and destination (customer); this is not the case with DS blocks… We need to carry out a comprehensive marketing campaign to promote and sell it, because each stone is different from another, and there are no two similar materials. Furthermore, neither customers nor architects know the origin of the stones and this has certainly led some operators to gain a hold over the markets, although this trend has lately been changed by the development of emerging countries and the large increase in DS international trading fairs and technical-business events. To set up a proper marketing strategy oriented to the end customer and dealer, which involves, among other factors, high expenses and strong efforts, we have to make sure that the product quality is controlled, that the producer is reliable and that the supply is regular and uninterrupted. Table 2 shows a typical distribution channel for a stone coming from a developing country, like Malawi, and going to a western country. The blocks are carried from the quarry to the importing western countries by truck, train and ship. The original ex-work price of 1 m3 (= production cost + producer overheads and profit) is increased by: export duties, custom duties, carriage costs (the highest ones), port or railway costs, brokerage fees, and costs for technicians who test and choose the blocks before exporting. The blocks are normally sold to big importing companies, sometimes (over the last few years) through a local broker, and get to Europe, at C.I.F. price, generally three times the production cost without any processing operation. Then, the company will sell the blocks (price increases by 20-30% of the C.I.F. price + brokerage fees, if any) to mayor processing companies or other importing companies. During this phase, many other people may enter the chain, and this is the reason of increasing the final price. 28

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Table 2. Example of distribution channel for an african granite (by M. Cosi)

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“The more direct the selling operations, the more competitive the product”. At least 35 m2 of slabs (2 cm thick) are produced from 1 m3 of granite. Finally, it must be noted that the dimension stone sector is like the “fashion” sector, where trends can change at any time. This specific situation allows several people to access the marketing and distribution channels (such as brokers, importers, carriers, consultants, etc.), who often take advantage of the above situation. Control over these channels, although really difficult, should be a primary target for a new producer.

2.5 Local, regional and international markets Markets and marketing (“how to approach a market”) are the most important factors for a DS stone project to be successful. A promoter should identify from the beginning (pre-investment phase) what potential the target material will have on the market and the target market itself. For an ACP promoter it is crucial to understand from the beginning how difficult or, often impossible it may be to launch on the international market a grey or pink granite, or a black granite with defects, or a non-absolute black exploited in “remote” areas, like most ACP countries. Apart from other factors which usually affect the viability of a commercial agreement (see quality control, continuous delivery, material homogeneity, etc.), this difficulty is generally due to high transport costs (local trucks and/or railway and sea freight), compared to the comparatively low end-sales prices of the above standard materials (generally ranging from 200 to 450/500 US$/m3). An ACP promoter who has a standard material should therefore have clear information and be aware of the potential prospects and trends of domestic and sub-regional markets. They often contribute to the success of a new project, without having to “live dangerously” on an overseas market. Regional markets in ACP countries have huge potentials: see, for instance, Western African countries (Senegal, Ivory Coast, Ghana or Nigeria) or Southern African countries (South Africa, Zimbabwe) or Kenya, Ethiopia and Sudan, where the building sector is impressively growing due to the recent discovery of large oil fields and the related high circulation of cash money. Finally, it is also important to consider other markets, which may often be closer and more approachable by ACP operators than the EU and USA markets, for instance, the Arabian countries (Saudi Arabia, Oman, UAE, Dubai etc.), the Middle East or the Far East, Japan and Taiwan. 30

PART 2

Understanding the stone industry

3. Trends in the use of dimension stone Throughout history, natural building stones and stone monuments have been the evidence of the cultural level of civilisations. Since pre-historic times, stones have been used in buildings and works of arts. Attributes of power and prestige were given to stones (monoliths and columns), probably due to their durability and impressive appearance. During the last 4,000 years, the use of valuable light-coloured, easilypolished stones, named “marble” (from the Greek word “marmaros” or “shining stone”), has become very important in Mediterranean, Middle-Eastern and Asiatic countries. In Africa, except for Egypt, important examples of historic use of stone are represented by the Great Zimbabwe ruins, from which the modern nation of Zimbabwe took its name, (Iron Age – around 1200 AD), and the stone circles of Senegal and Gambia (around 750 AD). Italy in particular, for both natural and historical reasons, has experienced the greatest development and concentration of marble production and processing activities in the world. After the 1950’s, the widespread use of reinforced concrete and other alternative and inexpensive materials in modern urban building developments led to a reduction in the use of stone. Furthermore, the traditional techniques for processing stone were anti-economical compared with those used for other materials. The last forty years have undoubtedly been a golden age for natural stone, with its long string of successes and rediscovery by architects and the design world. Yet, technological progress in the production and processing cycles has been a decisive factor and natural stone has in fact evolved into a real industry, albeit later than its rivals. From the beginning of the century, designers had preferred concrete, steel, glass and ceramics to natural stone, because of the lower costs, ready availability and easy installation of these materials. Natural stone was obviously at a disadvantage, since it was unable to cope with the large quantities required by the architectural world during that period which had to come to grips with the new mass societies and the need for large buildings as fast as possible. 31

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This discrimination was perhaps founded when quantity was the important factor, yet this did not stop it being used in great works of artistic value. Its use has harmoniously enhanced the poetic works of Mies Van Der Rohe with the German pavilion in Barcelona, Adolph Loos with Villa Karma and Terragni in Como, to name but a few. Thus, the belief that the ideals of the international modern movement and later movements were contrary to the use of stone is only partly true. In fact, when natural stone completed its technological evolution between the mid 60s and the mid 70s, it became a widely used material in world-wide architecture. Moreover, it was chosen then for its unique qualities. Technological progress has made stone more competitive in terms of production, but has also initiated a process of product transformation. This process is bound to have important consequences in the future, especially for architects who tend to follow three different trends: – Stone tradition; – Stone off-limits; – Stone innovation. There is still a large group of architects who conceive the use of stone essentially on its ornamental qualities (colour, vein patters, various decorations), yet not forgetting its material solidity. Only stone can guarantee the production of large units and the thickness required for long-term architectural projects which follow through to the final details of the building. Floors and facings always start off on the designer’s drawing board where they are created with specific shapes, joints and colour combinations for specific places and specific uses. The development of the production process has led to increasingly advanced machines, which can now cut to a thickness of less than 6 mm. Thus, stone maintains its unique ornamental qualities, but loses its solidity. Such exasperation is the result of competition. For stone to compete with rival materials, in addition to its range of unique colours and vein patterns, it needs to be lightweight too and this has become its most modern attribute. The reduction in thickness has led to a reduction in the size of individual units, which can now be considered as standard products, able to compete on a par with stone’s main rival, ceramics. So, the design criteria behind the use of these products is less focused on specific uses since they can be used without specific references. Finally, there is another trend which is currently gaining ground. This stems from the processes of technological innovation which highlight stone’s mechanical properties. Stone is, therefore, being used as a structural material again, though taking advantage of the new machinery and processes available. The innovation lies not only in 32

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Photo 13. The Ruins of Great Zimbabwe (by [email protected] and Dave Turkon – Mesa Community College).

the machinery, but also in a new philosophy which chooses to combine stone with other materials and products to create a unique product exploiting each material’s prime vocation. It is superfluous to state that the “two schools of thought” mentioned above, far from annihilating each other, can continue to develop separately from each other or even exist side by side if required by the project. Both, however, demonstrate the enormous industrial progress achieved by the stone sector, which has fully modernized to suit today’s applications and market requirements. In this sense, 33

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technological innovation in the sector has given a decisive contribution to both concepts of natural stone as a material and natural stone as a product, making them more competitive with rival materials and allowing them to be used for new applications at the same time, with obvious benefits in terms of higher consumption. Another important factor as regards stone innovation is its duality: it has increased the automation of production processes, now almost totally computerized, and it has improved craftwork, where the professional skills of those who carry out this work continue to be a necessary and decisive factor in achieving high-quality results.

4. Terminology and standards The term “dimension stone” commonly refers to “a natural building stone” that has been selected, trimmed or cut to specified shapes or sizes with or without one or more dressed surfaces. This definition applies to rough blocks, slabs and polished stones used mainly in building, construction, monument and funeral art. Ornamental and precious stones for jewellery and crushed stone for use as aggregate or powdered materials are not classified as dimension stones. There is a commercial classification of dimension stones very different from the scientific classification of rocks and, consequently, without clear definitions.

4.1 Geological classification In Earth Sciences, rocks are classified according to their common origin, regardless of their macroscopic appearance, physical properties, fabric, mineralogical and chemical composition, which are considered as less important for the geological classification of rocks. To the geologist, any mass of mineral matter, whether consolidated or not, produced by natural processes either on earth or anywhere else in the universe, is a rock. Rocks usually consist of aggregates of one or more mineral species. A mineral is a structurally homogeneous solid (except native mercury) with a definite (not necessarily constant) composition formed by inorganic processes. Rocks are divided into three main groups according to their origin: 34

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• IGNEOUS ROCKS These are produced by the cooling and crystallisation of silicate melt (magma) on the surface of the earth (extrusive rocks) or inside the earth (intrusive rocks). Generally speaking, igneous rocks have a crystalline appearance, although non-crystalline igneous rocks do occur. They include: basalt, gabbro, granite, syenite, diorite, anorthosite, etc. • SEDIMENTARY ROCKS These are rocks formed from materials derived from pre-existing rocks by processes of denudation together with material of organic origin. The term includes both consolidated and unconsolidated material; the process of conversion of unconsolidated to coherent sedimentary rocks is called diagenesis. Sedimentary rocks are classified according to the process which led to their deposition: – clastic (breccias, conglomerates, sandstone, shale, etc.); – organic (limestone, dolostone, chert, coal, phosphates); – chemical (evaporites, travertine, etc.). • METAMORPHIC ROCKS These resulted from the transformation of pre-existing rocks by heat, pressure and fluids within the earth’s crust. Metamorphic processes are considered as taking place in the solid state and involve re-crystallisation, changes in the fabric and mineralogical and chemical composition of the parent rock. Some of the most common metamorphic rocks are gneiss, mica schist, amphibolite, migmatite, phillite, marble.

4.2 Commercial classification Commercial definitions of rock types derive from their quality (durability, strength, etc.) and the techniques required for their processing. In a very broad sense, “marble” includes any rock which can be polished, whereas a “stone” cannot be polished. More accurate definitions, grouping together the terms most commonly used in the stone market, are as follows: • MARBLE – a rock mainly composed of minerals with a hardness of 3-4 on the Mohs’ scale, for example calcite, dolomite and serpentine.

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All carbonate rocks, such as true marble (metamorphic carbonate rock), limestone, dolostone, calcareous breccia, etc., belong to this category. Alabaster, onyx, serpentine, and ophicalcite belong to this category too. • GRANITE – a rock mainly composed of an aggregate of visible crystals, the hardness of which is 7 or 8 on the Mohs’ scale, for example quartz, K-feldspar and plagioclase. In commercial jargon, granite includes: granite, syenite, granodiorite, diorite, monzonite, gneiss, migmatites and porphyry ignimbrites and porphyry subvulcanic rocks. Gabbro, dolerite, charnockite, anorthosite also fall into this category. • STONE – any rock which cannot be polished is regarded as being a “stone” in the commercial usage. Therefore, the term stone may include: calcarenites and sandstone with low or medium diagenesis level; volcanic and pyroclastic rocks, such as basalt and tuff; metamorphic rocks, such as micaschists, gneiss, shale and slate. All the naturally cleft stones belong to this group. Granite and marble, as defined above, are always easy to distinguish from each other. They have, in fact, different applications according to their physical and chemical properties and appearance. Granite is often used for exterior works, mainly for cladding buildings, due to its durability. It is however also used for interiors, such as floorings in commercial buildings, where high resistance to intense foot traffic is required. Marble is mainly used in interiors, due its lower resistance to environmental agents. In current commercial jargon, rock varieties are identified by fanciful names derived from certain aesthetic features or, alternatively, by well-established names after specific places. For instance, names such as Botticino, Pentelikon, Syenite, refer to places; whereas Nuvolato (cloudy), Fior di Pesco (peach flower), Bardiglio, Multicolour are taken from the peculiar aesthetic attributes of the rocks. Sometimes, the name of a stone variety includes terms related to the geological classification of the rocks which may or may not coincide with the accurate scientific name of the rock. Some other times, the same name is referred to different stones, or similar varieties are referred to with different names. This is often misleading for a proper qualitative determination of rocks. The correct identification of dimension stone should include the commercial name or names, the geological definition of the rock, the quarry location, the technical features and photographs on a 1:1 scale 36

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of a standard polished sample showing the range of variation, if any. According to the new European Norm “EN 12440 Natural Stones – Denomination Criteria”, dimension stones will be described by the following: traditional commercial name, scientific name, range of colour and place of origin. Process conditions, natural features, petrographic name and geological age can also be added. This norm also states that in giving a name to a new material, geographical names not related with the actual place of origin of the stone and company names shall be avoided.

4.3 Reconstructed stone Dimension stones result from the processing of whole blocks as they come from the quarry, whereas reconstructed stone refers to aggregates of pieces of natural stone with various grain sizes cemented together in a pack structure by a synthetically-made matrix (cement or polyester resin). In some cases, reconstructed stones are very similar to natural stones in their macroscopic features: they have good mechanical properties, making their range of applications comparable to that of dimension stone. Some designers and engineers do not like to use reconstructed stone for the exteriors of buildings because of the matrix’s poorly tested resistance to weathering. “Terrazzo” is the most popular type of artificial stone. It is made of cement and marble with extra marble chips on the surface. In more modern versions, the cement portion is replaced with synthetic resins, such as polyurethane or epoxy. Over the last few years and as a consequence of the growth of the dimension stone market, many new types of artificial stone using polyester resin as the grain matrix have been promoted and successfully used in constructions.

4.4 Specifications, tests and analyses The recent demand for a wide range of stone varieties with different physical properties, such as colour, texture and grain size, has led to an ever-lasting increase in the number of commercial types of dimension stones throughout the world. This is essentially due to quick changes in the aesthetic tastes for the architectural design of buildings. The availability of an increasing number of new stone types on the market and the wider range of applications of stones in modern architecture have given rise to the need to develop dimension stone spec37

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ifications obtained by testing in order to define the technical properties of dimension stones. Specifications for dimension stone are becoming more and more demanding as stone is used in new and challenging applications. Users are demanding guarantees that the chosen material will perform as promised by the seller, with no bad surprises after installation. This has resulted in an increase in the demand for quality control testing in an effort to reduce liability in the use of stone products for buildings and to guarantee safe stone applications. For building and construction applications, for instance, stone should be able to resist stress from structural, wind and seismic loading; it should not absorb too much water, moisture or other fluids, since the freeze-thaw cycles in colder climates would cause spalling. A stone product should resist staining or discoloration from exposure to water and should wear evenly when subject to intense foot traffic, etc.

4.4.1 Physical-mechanical tests In the attempt to define these and other physical properties of dimension stone, many standard testing methods have been developed. Unfortunately testing methods differ from one country to another as do the results for the various physical properties measured using different testing procedures. The differences in testing methods concern the size of test samples and the testing technologies used for determining the physical properties of certain rocks. The CEN TC 246 “Natural Stone” Technical Committee, composed of stone specialists from the member states of the European Union, has been working to set up standards for natural stone building materials since 1990 (see Table 3). In particular, CEN TC 246 consists of three working groups: WG1 – Terminology, classification and properties; WG2 – Test Methods; WG3 – Product specifications. The results of WG2 will lead to a common determination of the physical-mechanical properties of natural stones to be enforced throughout the EU. Other European Technical Committees partly dealing with natural stone are TC 125 on Masonry, TC 128 on Discontinuous Roofing and Cladding Products and TC 178 on Paving Units and Kerbs (see Table 4). In the United States, and in its economically linked countries, rock specification procedures are provided by the ASTM – American Society for Testing Materials (see Table 5). The most important physical properties of dimension stone which are 38

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Table 3. European standards for natural stones – prepared by the CEN/TC 246. CODE

TITLE

Availability

Determination of Resistance to Salt Crystallization Determination of Frost Resistance Determination of Flexural Strength under Concentrated Load Petrographic Examination Denomination Criteria Terminology Determination of Flexural Resistance (under Constant Moment) Determination of the Breaking Load at the Dowel Hole Determination of Geometric Characteristics on Units Determination of Water Absorption at Atmospheric Pressure Determination of Slip Coefficient Determination of Water Absorption Coefficient by Capillarity Determination of Compressive Strength Determination of Real Density and Apparent Density and of Total and Open Porosity EN13919 Determination of Resistance to Ageing Actions by SO2 in presence of Humidity prEN 12057 Finished Products, Modular Tiles – Specifications prEN 12058 Finished Products, Slabs for Floors and Stairs – Specifications prEN 12059 Finished Products, Dimensional Stone Work – Specifications prEN 14066 Determination of Thermal Shock Resistance prEN 14146 Determination of Dynamic Elastic Modulus (by Fundamental Resonance Frequency) prEN 14147 Determination of Ageing by Salt Mist prEN 14157 Determination of Abrasion Resistance prEN 14158 Determination of Rupture Energy prEN 14205 Determination of Knoop Hardness prEN 14579 Determination of the Sound Speed Propagation prEN 14580 Determination of Static Elastic Modulus prEN 14581 Determination of Thermal Dilatation Coefficient prEN 1467 Rough Blocks – Specifications prEN 1468 Semi-Finished Products (Rough Slabs) – Specifications prEN 1469 Finished Products, Slabs for Cladding – Specifications prEN WI 246030 Determination of Surface Finishes (Rugosity)

published published published published published published published published published published published published published

EN 12370 EN 12371 EN 12372 EN 12407 EN 12440 EN 12670 EN 13161 EN 13364 EN 13373 EN 13755 EN 14231 EN 1925 EN 1926 EN 1936

published published 2003-06 2003-06 2003-06 2002-12 2003-01 2003-09 2003-09 2003-09 2003-09 2003-09 2003-09 2003-09 2003-06 2003-06 2003-06 deleted

EN = European Norm prEN = Project of European Norm

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Table 4. Other european standards for natural stones. CODE EN 1341/2001 EN 1342/2001 EN 1343/2001 prEN 12326-1 EN 12326-2/2000 EN 13242/2002 EN 13383-1/2002 EN 13450/2002 EN 13383-2/2002 prEN 771-5 EN 771-6/2000

TITLE Slabs of Natural Stone for External Paving CEN TC Requirements and Test Methods 178 WG2 Setts of Natural Stones for External Paving Requirements and Test Methods Kerbs of Natural Stones for External Paving Requirements and Test Methods Slate and Stone Products for Discontinous Roofing and Cladding - CEN TC Part 1: Product Specification 128 SC8 Slate and Stone Products for Discontinous Roofing and Cladding Part 2: Methods of Test Aggregates for Unbound and Hydraulically bound Materials for CEN TC Use in Civil Engineering Work and Road Construction 154 SC4 Armourstone - Part 1: Specification Aggregates for Railway Ballast Armourstone - Part 2: Test Methods Specification for Masonry Units CEN TC Part 5: Manufactured Stone Masonry Units 125 WG 1 TG6 Specification for Masonry Units Part 6: Natural Stone Masonry Units

EN = European Norm prEN = Project of European Norm

generally considered and defined by most standard testing laboratories are the following: – apparent density (bulk specific gravity); – compression strength; – flexural strength; – abrasion resistance; – energy of rupture by impact; – water absorption; – thermal coefficient of expansion. The apparent density (or bulk specific gravity) is the ratio of the weight of a dried rock sample of a given shape and size to its volume, expressed in kg/m3. For carbonate rocks, including marble, apparent densities range from 2,500 to 2,700 kg/m3; for most granites, it is 2,700 kg/m3 and up to 3200 kg/m3 for some gabbros and ultramafic rocks.

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Table 5. American standards for dimension stone prepared by the ASTM C-18 CODE

TITLE

C 615-99 C 568-99 C 503-99 C 616-99 C 406-00 C 629-99

Specifications for Granite Dimension Stone Specifications for Limestone Dimension Stone Specifications for Marble Dimension Stone (Exterior) Specifications for Quartz-based Dimension Stone Specifications for Roofing Slate Specifications for Slate Dimension Stone

C 241-90* C 97-96 C 170-90 (99) C 880-98 C 120-00 Elasticity) C 99-87 (00) C 1201-91 (96)

Test Method for Abrasion Resistance of Stone Subjected to Foot Traffic Test Method for Absorption and Bulk Specific Gravity of Dimension Stone Test Method for Compressive Strength of Dimension Stone Test Method for Flexural Strength of Dimension Stone Test Method for Flexure Testing of Slate (Modulus of Rupture, Modulus of

C 121-90 (94) C 217-94 C 1352-96 C 1353-98

C 119-00 C 1242-00

Test Method for Modulus of Rupture of Dimension Stone Test Method for Structural Performance of Exterior Dimension Stone Cladding Systems by Uniform Static Air Pressure Difference Test Method for Water Absorption of Slate Test Method for Weather Resistance of Natural Slate Test Method for Flexural Modulus of Elasticity of Dimension Stone Test Method for Abrasion Resistance of Dimension Stone by the Taber Abraser Test Method for Strength of Individual Stone Anchorages in Dimension Stone Terminology relating to Dimension Stone Guide for Design, Selection and Installation of Exterior Dimension Stone Anchors and Anchoring System

Note: the first part of the code, such as C-615, represents its fixed designation; the number immediately following the designation indicates the year of original adoption or, in case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. An * indicates an editorial change since the last revision or reapproval.

The strength of a rock is its ability to resist loading stresses. In testing the strength of a dimension stone, the applied stress may be uniaxial, or uniaxial after freeze-thaw cycles. The latter test provides important information on a rock’s ability to resist prolonged exposure to colder climates. Flexural strength is a measure of the rock’s resistance to bending. This test should be conducted even after freeze-thaw cycles. Rock strength testing tools vary from one testing method to another. The units of rock strength are the same as those of pressure. 41

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The orientation of samples is crucial in all tests on rock strength since most rocks show intrinsic mechanical anisotropies. These are induced by bedding and depositional structures in sedimentary rocks, fracturing and residual elastic stress in all deformed rocks, cleavage and schistosity in metamorphic rocks, and other structural anisotropies of different grains (see rift planes in granite). The average values of compression strength range from 60-80 MPa for sandstone and some limestones, to 100-130 MPa for granite, marble and some gneiss and to > 200 MPa for quartzite, serpentinite and other metamorphic rocks. Abrasion resistance is the difference in thickness of a given rock sample before and after it undergoes a monitored abrasion test using a special polishing machine called tribometer. This physical property is determined by the composition, grain size and texture of the rock and it is very important for the assessment of the potential use of a stone in certain applications, such as interior and exterior floorings, where the scratching resistance of a stone product is crucial. The energy of rupture by impact defines the fragility of a rock. This is obtained by measuring the minimum height, usually in centimetres, of a falling metallic sphere (normally of 10N) which breaks up stone slabs of given sizes. The values of energy of rupture by impact vary depending on the size of the stone slabs used in the test. Water absorption is the ratio of a dried sample to the same sample saturated with water. This parameter depends on the porosity of the rock and its magnitude is related to the rock’s ability to resist frost and weathering. The thermal expansion coefficient is the dilatation in millimetres per unit length and degree Celsius of a rock sample of given size and shape during heating and cooling cycles. This measurement uses a special equipment called dilatometer. Other important physical properties frequently tested in stone specifications are: micro-hardness, measured in MPa using a Knoop penetrometer, which provides indirect information on a rock’s behaviour during sawing; elasticity modulus (MPa), which is directly linked to a rock’s fragility; rock solubility or resistance to chemical agents, which is very important for the use of stone in polluted environments, like urban areas. Although there are no definite criteria for the establishment of a direct relationship between the physical properties of a stone and its potential uses, empirical information or broad qualitative stone classifications are usually consulted by users for this purpose. The Marble Institute of America (MIA) has classified the “degree of soundness” for commercial marble based on the features determined by the producer as the blocks are quarried and fabricated. According 42

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to this classification, the degree of soundness for marble is classified into four groups – A, B, C, and D. They only describe what method and amount of repair and fabrication is necessary for each group before or during installation. ASTM provides well-defined values for the physical properties of rocks that correspond to the tolerance limits (minimum or maximum) required for stone applications. Other basic physical properties of dimension stones, such as colour, translucence and texture, depend on their unique grain, i.e. their mineralogical and chemical composition. The optical properties of a rock, such as colour, translucence, etc., which are fundamental features for dimension stones, depend on the composition of the mineral species and the groundmass which forms the rock. The visual properties of minerals are determined by the presence of chemical impurities in the mineral, such as iron oxides and hydroxides, or by simple changes or distortions in the crystalline structure. Each mineral species may show a wide variety of visual properties that, in turn, influence those of the constituting rock. As far as colour is concerned, for instance, calcite may be white, yellow or green; feldspar is white, pink, red, green, dark grey, etc. The mineralogical composition and compactness of a rock and the cohesion between its crystal grains determine whether or not it can be polished. All the rocks which are commercially known as marble can be polished, regardless of the type of rock, fabric and texture. A comparatively high clay mineral and mica content in sedimentary and intrusive rocks, the presence of a microcrystalline matrix in volcanic rocks, high porosity and low cohesion are some of the chief factors which limit the possibility of polishing a rock. True marble, as scientifically defined, can always be polished, except when the clay mineral content (impurities of marble) is high.

4.4.2 Petrographic and chemical analyses. Petrographic and chemical analyses are necessary for a correct classification of rocks and to provide information on the rock composition. Such analyses may facilitate the survey of compositional or structural differences between similar rock types that may correspond to different behaviours in specific uses. The petrographic analysis includes both manual observations of specimens and a microscopic analysis of a thin section of the rock. Macroscopic observations are focused on defining texture, grain size, micro-fracturing, weathering conditions and other rock characteristics. 43

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The microscopic analysis of a rock (thin section of about 25-30 mm thickness) is carried out by means of a mineralogical microscope equipped with a polarizer. Microscopic observation shows the mineralogical composition and structural shape of a rock. Important information can also be obtained on the discontinuities (pores and microfractures) and weathering conditions. The chemical analysis of dimension stones considers the major elements. Other elements may be determined and quantified upon request. The main elements analysed (as oxides) are the following: SiO2, Al2O3, Fe2O3, FeO, MgO, CaO, Na2O, K2O, TiO2, P2O5, MnO. The results of the petrographic and chemical analyses lead to an accurately scientific classification of a rock.

5. Geological description of the dimension stone deposits The identification of a dimension stone deposit is determined by the quarrying conditions of the deposit, as summarised hereafter: – presence of one or more rock types of potential or ascertained commercial quality; – extensive reserves characterised by rock consistency, i.e. without significant changes in colour, texture, etc.; – low fracturing, which allows for the exploitation of sizeable blocks with acceptable recovered blocks-to-waste ratio; – favourable morphologic conditions, i.e. soil or sterile weathered overburden of reduced thickness; – logistical accessibility, presence of infrastructure and other “intangible” factors. Most of these conditions are related to the geological characteristics of the deposit. The knowledge of these features is a basic point for the identification of any potential dimension stone deposit. Complete accounts of the geological characteristics of dimension stone deposits are dealt with in Earth Sciences textbooks as special topics. The origins and processes involved in the formation of a dimension stone deposit have to be fully understood to decide upon its economic exploitation. For the purpose of this guide, a short account on the nature of some features observed in dimension stone deposits is given below. 44

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5.1 Carbonate rock deposits Carbonate rock includes both sedimentary carbonate and crystalline marble (“true marble”), which is a metamorphic rock. According to the commercial definitions of dimension stone, both these rock types are regarded as being marble if they have a nice appearance and can be polished. Carbonate rock that cannot be polished may also be used as a dimension stone. These particular types of carbonate rock are commercially defined as “tufa”. If found in large quantities with consistent characteristics, even thinly bedded, they may be used for cladding surfaces in urban areas or as construction stones. The most common “tufa” are highly porous and soft carbonate rocks. 5.1.1 Sedimentary carbonate deposits In sedimentary carbonate rocks used as dimension stones, both the physical properties and deposit consistency are determined by two main genetic factors: the depositional environment and the diagenetic processes. The understanding of these two factors helps to predict the deposit consistency. The depositional geometries, bedding, sedimentary structures and texture of the stone, all depend on the type of environment where the carbonate rock sequences were formed. a) Depositional environments These provide a vast area of research that includes the study of modern environments where carbonate sediments currently form and culminates in the recognition of depositional environments of carbonate rocks formed in the past. Carbonate depositional environments fundamentally differ from their terrigenous counterparts, since carbonate particles are the direct product of organic or chemical precipitation. Carbonate sediments and rocks are formed by whole or fragmented skeletal grains of aragonite or magnesian calcite produced by benthic organisms, such as corals, molluscs, echinoids and calcareous algae (carbonate mud) in shallow, tropical environments. They are also formed in the upper 200 m of open oceanic waters that are not limited in latitude, where pelagic and planktonic organisms secrete calcite shells. Carbonate depositional environments are classified according to their physiography and depositional products. These are: sub aerial exposure, lacustrine, aeolian, tidal flats, beach and shelf, reef, and basin margin and pelagic environments.

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Sub aerial exposure Valuable dimension stone deposits, such as travertine and onyx, form in a sub aerial environment. In addition, karst structures, which originate from the sub aerial exposure of carbonate bodies, represent one of the most important geomorphologic features in many carbonate deposits. Travertine is an accumulation of calcium carbonate in springs (karstic, hydrothermal), small rivers and swamps that mainly forms by encrustation (chemical or biochemical precipitation). The term travertine comes from Tiverino, the old Roman name of Tivoli, in Italy, where travertine can be found in extensive deposits. For the precipitation of calcium carbonate to occur, water must reach a high concentration of CO2 and Ca2+ and there must be a reduction of CO2 in the water. This reduction occurs as the temperature increases and the pressure decreases in the water. Vegetal activity also regulates the rate of CO2 in water and, hence, calcite precipitation. Travertine has a laminated, radial and arborescent fabric and is often characterised by a high porosity. Vegetal encrusted remains are often visible in travertine. The travertine bodies are laterally discontinuous, since their depositional geometry is controlled by the shape of the substratum or host rock, where the precipitation of the calcium carbonate occurs. Deposits of travertine are found as tabular bodies fractures or cavefilling material, or very thin rock encrustations. However, it is not so rare to find travertine in economically exploitable deposits where large volumes of calcium carbonate may have precipitated and accumulated. The term karst is used to refer to specific landforms and geographic regions where these landforms occur. Karst consists of an overprint in sub aerially exposed carbonates, produced and controlled by the dissolution and migration of calcium carbonate in meteoric waters, occurring in a wide variety of climatic and tectonic settings. Karst features are recognisable as surface landforms, such as lapies, dolinas; subterranean features, such as caves, pipes, voids; collapse breccias due to the removal of underlying carbonate; speleothems (flowstone, stalagmites, stalactites, globulites, cave pearls, etc.). As a residual product of carbonate dissolution, “terra rossa” or red soils are typical deposits of karst regions. In sub aerially exposed carbonate sequences, karsts evolve with early to late stage features. Heterogeneities such as fractures, joints, bedding, impurities in the carbonate host and vegetation favour the development of subterranean landforms. As a result, the surface evolves into complex landforms, such as dolinas, 46

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uvalas, karst valleys and plains. In tropical climates, the increased accentuation of the surface morphology produces conical and tower karsts. Speleothems with uniform, massive structures may constitute valuable dimension stone deposits of onyx. The various types of onyx differ in colour, composition (which may vary from aragonite to low-magnesian calcite), fabric (microcrystalline, medium to coarse crystalline fabric) or texture (tabular or globular laminae, bedded or radially arranged crystals, microcrystalline masses, etc.). Although some onyx varieties have a high economic value, due to the scarcity and small size of the deposits, mostly found as cavity or fracture filling materials, the uses of onyx are limited to the fabrication of novelties and furniture objects.

Photo 14. Eritrea: illustration of a black marble quarry (by P. Primavori).

Lacustrine Carbonate rocks deposited in Photo 15. Zambia: karst structures in a white crystalline marble lacustrine environments may quarry (by P. Primavori). form dimension stone deposits, although comparatively unimportant. Chemical or biochemical precipitation of calcium carbonate may occur. Lacustrine carbonates are fossiliferous, if fresh water mollusc fragments are contained within the carbonate mud. Alternatively, carbonate looks thinly laminated if deposition is controlled by algae or rhythmic chemical precipitation, such as in varve deposits. Algal laminations are planar or convolute and are also designed as “stromatolite”. Other important carbonate precipitates produced by algae activity are pisoliths and oncolites, which are spherical encrustations characterised by a concentric lamination. All these sedimentary structures can be found as distinguishing 47

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marks of lacustrine carbonate, and may also represent interesting features for applications as dimension stones. Aeolian Wind-deposited carbonates mainly occur in dry climates. Although they form common and conspicuous facies nowadays, few aeolian carbonates are found from ancient rocks. Carbonate dune sands, which line coastal areas where abundant carbonate sand accumulates, are difficult to recognise because of their similarity to carbonates deposited in high-energy shallow marine environments. Calcareous aeolianites are characterised by a high degree of grain sorting; grain size is fine to medium. Well-developed cross stratification, which is typical of dune formations, is often found in carbonate aeolianites. The cementation of aeolianites is related to the percolation of meteoric water through the pores of carbonate dunes. Due to the low degree of cementation, some Pleistocene or Holocene carbonate aeolianites are an economically good source of tufa. Tidal flats Tidal flats are an important source of many types of sedimentary carbonates used as dimension stones. Most fine-grained and thin-laminated limestones and dolomites are generated in this type of environment. Their colour is usually beige. Thin lamination is the result of algal activity (stromatolites) in tidal flats and is the dominant structure of many carbonate dimension stones (examples: Trani, Serpeggiante – Italy). Fossils, micrite intraclasts and burrows are commonly found in carbonates formed in this environment. They are arranged in different grain packing within a micritic matrix and their occurrence in carbonate dimension stone may represent an aesthetically pleasant feature. Porosity is comparatively high and is a distinguishing characteristic of supratidal carbonates. Pores may be filled with calcite crystals. Depositional geometries of tidal flats are characterised by persistent flats and thick beds. Another important depositional product of tidal flats is anhydrite that, if deposited in nodular masses of a comparatively large volume and rehydrated, are a source of alabaster deposits. Alabaster consists of microcrystalline or saccaroidal aggregates of gypsum and is usually white or brownish-coloured. Carbonate or clay impurities may lead to various types of aesthetically pleasing textures of alabaster. Due to its limited hardness – 2 on the Mohs’ scale –, alabaster is a valuable material mainly to be used in the fabrication of novelties. 48

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Beach and shelf environments Thick and laterally extensive carbonate sequences form in beach environments. These are characterised by well-sorted grains, due to the high energy of the depositional processes, such as waves, tidal and shore currents. Typical sedimentary carbonate structures deposited in beach environments are cross-bedding and parallel laminations. In lower energy sub-environments, such as offshore portions of beach, biogenic burrows and shell fragments are also found in carbonates. Conspicuous deposition of high-energy carbonate particles, such as ooids, is recorded in beach environments. The resulting carbonate rock consists of hard grain stone and forms very sound beds exploited as sources of dimension stone of high quality and is the source of marble, since it polishes well. Due to the high degree of oxygenation of this environment, the most common colours of carbonate formed in beaches are light beige, yellow or white. Shelf environments include lagoons or restricted bays enclosed by barrier islands or reefs. In these environments, monotonous, fine-grained carbonate (mudstone and wake stone) may form extensive deposits. Carbonate deposited in shelf environments is characterised by an abundance of bioturbation and a limited variety of biogenic fragments (fossils), although these may form a significant part of the rock. Evaporites and dolomites may also develop in shelves and represent a diagnostic marker for shelf environments if found within a carbonate sequence. The depositional geometry of restricted carbonate settings may range from simple level-bottom expanses to complex compartmentalised environments, where depositional reliefs have developed. Due to restricted water circulation, the concentration and preservation of organic matter and precipitation of sulphides in carbonate sediments occur in shelf environments. Hence, the colour of the resulting rock is often dark brown or grey. Many rock types of this group are used as dimension stones. Decorative, poorly sorted fossiliferous packstone and wakestone of various colours (beige, grey, brown, black) are common on the dimension stone market as valuable marble varieties (examples: Perlato, Blue Mediterraneo, Pietra Leccese, Portoro, Botticino – Italy and Nero Marquina – Spain). Nodular structures in carbonates, which are generated in this kind of environment by intense bioturbation and burrowing, are also appreciated decorative features of dimension stone. 49

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Reef environments Reef and adjacent environments include a wide variety of depositional systems and are the main source of carbonate rocks which may constitute important dimension stone deposits. A reef is the physical expression of a community of calcium carbonate-secreting organisms, such as corals, echinoids, bivalves, calcareous algae, etc., growing in one place over a long period of time. Many types of carbonate generated in reef environments are bio-constructed, i.e. entirely formed by large fossils that form the supporting framework of the rock. Reefs also consist of in-place accumulations of fine-grained calcium carbonate of calcareous algae or carbonate skeletal fragments. Carbonate rocks of reef environments vary laterally according to the area of origin. Reefs may constitute natural barriers between the open ocean and inland shelves. Transitional areas are characterised by different types of carbonate deposition. Back reef areas, for instance, are dominated by fine-grained and fossiliferous carbonates deposited in comparatively calm conditions. Near the seaward edge of the reefs, large quantities of carbonate sand are accumulated in high-energy conditions. The resulting rock types are often composed of well-sorted oolitic grainstones, which may constitute exploitable good-quality dimension stone. In fore-reef areas and slopes, well-sorted bioclastic carbonates and breccias are also accumulated. These rocks are valuable as dimension stones. Slope carbonate deposits are characterised by a wide range of lithologies, composed of transported reef and shelf debris and interbedded with basinal-mud deposits. Gravity-induced depositional structures, such as talus blocks, slump, debris-flow and turbidite, are clearly recorded in these types of carbonate. Massive carbonate build-ups can also develop in deep ocean environments. Both modern and ancient reefs have different shapes and sizes. There are, for example, pinnacle-shaped reefs, patch reefs and table reefs. The reef type may also be recognisable from the rock record. Biological components may also differ from one reef to another. Reefal carbonates are identified by their massive structure, types of fossils, texture, porosity and the internal sediment and cement. All these characteristics are of particular importance in the use of carbonates from reef environments as dimension stones. Unfortunately, the exploitation of these deposits is often limited by rapid facies changes and variable depositional geometries, due to the complexity of reef environments.

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Basin Margin and Pelagic environments Carbonate slope bases gradually merge with oceanic basin floors. These environments are characterised by fine-grained hemipelagic and pelagic sedimentation. The mass transport of sediments and soft sediment deformations of various grain sizes – i.e. debris flows, slides and slumps – commonly occurs at the base of slopes and continental rises, whereas in abyssal floors very fine-grained sediments are the dominant depositional product of turbidity currents or simple precipitation of planktonic organisms. Carbonates formed in these environments are usually thin and regular-bedded, alternating with clay or marl. Chalk deposits in central Europe are composed of pelagic carbonates. Bioturbations and hardgrounds are the origin of the nodular structure that is commonly found in pelagic carbonates. Some nodular carbonates in pelagic environments are exploited as valuable dimension stones (example: Rosso Verona, Rosso Magnaboschi, Rosso Sicilia – Italy). Secondary chert is abundant in places within the carbonate beds of pelagic environments. Chert may be the dominant component of pelagic sediments, and radiolarites are the result of the pelagic sedimentation of silica organisms below the carbonate compensation depth alone. Red, yellow, green or black-coloured radiolarites are used as ornamental stone. b) Diagenesis Diagenesis refers to all processes occurring in the proximity of the Earth’s surface that lead to the formation of a massive rock from loose sediment. Diagenetic processes involve the partial modification or even total disruption of the sedimentary structures belonging to the original sediment by compaction or burrowing; the development, migration and concentration of certain chemical compounds (oxides, sulphides, etc.); the cementation of the grains of the sediment; the partial or total conversion of a mineral compound to another, such as in dolomitization. This last process must not be confused with metamorphism, which takes place as a result of increased temperature and pressure further below in the Earth’s crust. In sedimentary carbonates, diagenesis plays an important role in determining the physical properties of the rock that constitute valuable characteristics for dimension stone use. For instance, some colour or texture changes in carbonates are determined by diagenetic processes. It is difficult to predict these changes, due to the random distribution of diagenetic features in carbonate 51

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sequences. Diagenetic structures may also be valuable ornamental characteristics of dimension stones. Early diagenetic structures, such as the recrystallisation of metastable aragonite or magnesian-calcite into stable calcite or dolomite, often improve the characteristics of the carbonate rock in terms of dimension stone requirements. Stylolites are also a common type of diagenetic structure of sedimentary carbonates. They are irregular suture-like joints, that may develop in carbonates either parallel to the beds or independently of the bedding plane. Stylolites are formed by the pressure-controlled solution of carbonate following its diagenesis. Red clay, organic matter, iron oxides or other residual solutes are concentrates within stylolites sutures. Stylolites can develop as a result of the burial by an overlaying rock sequence or, alternatively, by tectonic stress, or both processes in carbonate. Stylolites may be considered as a decorative feature, especially if the filling residual material is coloured (usually red or yellow), and may increase the value of the carbonate rock used as a dimension stone (examples: Filetto Rosso, Filettato – Italy and Rosa Atlantide, Alpinina – Portugal). Alternatively, stylolites may constitute a limit for the carbonate rock to be used as a dimension stone. An excessive mechanical weakness may, in fact, develop along the stylolitic joints that may, in turn, increase the rock’s fragility. Dimension stone deposits of sedimentary carbonates are massive or bedded. Beds, if sufficiently thick and regular, may facilitate block removal, since their lower and upper limits always represent pre-existing surfaces that are mechanically weak and can be exploited for benching. The bed geometry and types of sequences in limestone or dolostone deposits are both determined by the depositional environment. The bed attitude is the result of a tectonic displacement, if this differs from the horizontal. In most sedimentary carbonates used as dimension stones (limestone or dolostone), the bedding attitude is horizontal or near to the horizontal, and the surfaces of bed discontinuity are exploited for limiting either the foot or roof wall of benches, or both. Beds may also appear to dip gently or steeply, or even overturn; they are also involved in folds and faults, that are often observed in areas of strong tectonic deformation. Brittle deformation causes fracturing in carbonate beds. The term fracture designates all types of surfaces of physical discontinuity, except bedding, which separate the rock mass into fairly large-sized portions. Therefore, fractures include faults, joints, cleavage, etc. Fracturing systems in carbonates, as in other types of dimension stone deposits, are a determining factor for the quarrying conditions. 52

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When carbonate beds are thick and regularly fractured, with fractures perpendicular to the bedding, the removal of blocks is facilitated by the presence of these fractures. Generally speaking, in sedimentary carbonate deposits, the only preferential factors that make for easier splitting are represented by the bedding and other fracture systems perpendicular or almost perpendicular to bedding. In carbonate deposits, both bedding and fractures represent the most common types of uniformity where karst features may easily develop. Karst topography is a characteristic feature of many carbonate deposits. However, the excessive development of surface or subterranean karsts may reduce the extent to which carbonate deposits may be quarried. In sedimentary carbonate deposits, the geometry and attitude of beds, the fracturing system and the karst features dictate the best quarrying method. Non-systematic fracture systems in carbonate may be cemented by transparent calcite to form a network of calcite veinlets, that may be a favourable decorative feature. If well cemented, some fault breccias made up of carbonate clasts may be valuable dimension stones (examples: Breccia Pernice, Breccia Aurora – Italy and Breche Nouvelle – France).

5.1.2 Marble deposits Marble is a metamorphic rock formed by the recrystallisation of sedimentary carbonate. Marble ranges from pure calcium carbonate to dolomite, including all the intermediate compositions. Pure white marble is brilliant white, hence the greek root “marmaros” which means shining (examples: Thassos, Dionysos – Greece and Statuario – Italy). Uniform colours of marble, i.e. light green, light blue, pink, etc., are determined by the presence of cations in the calcium or magnesium carbonate molecules, such as iron, manganese, zinc, strontium, etc., although defects or distortions in the crystalline structure of calcite may be responsible for the different colours of marble varieties. Shades ranging from very light grey to black are produced by disseminated organic matter or sulphides (example: Bardiglio – Italy). Green tints result from the presence of chlorite or other silicates, such as epidotes. Pink and red marbles owe their colour to the presence of hematite, manganese carbonate (example: Pink Portugal – Portugal) and yellow and cream marbles to small quantities of iron hydroxides (limonite). The size of crystals in marble ranges from very fine, almost invisible to the naked eye, to coarse (in the region of 5 mm). In most marble, 53

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Photo 16. Vertical cut performed by a chain saw in a marble quarry in Namibia (by P. Blasi).

the grains are irregular and closely interlocked and show random orientation. The soundness of a peculiar marble is determined by intergranular cohesion and low porosity. These are indispensable properties, that make marble valuable for dimension stone applications. Both colour and crystalline fabric of marble may be evenly distributed, although in many marble deposits they are found in mottled patterns, or in bands called “veins” (example: Bianco Carrara – Italy). Silicate impurities in the form of mica and chlorite are generally scattered in dark patches and bands throughout the marble mass. These impurities may create a pleasant pattern or weaken the marble and reduce its value, since it does 54

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not polish as well as pure marble does. Quartz veins or patches may be present in marble as its primary component or produced by metamorphic segregation, migration from other rocks. Silica veins and patches often give the marble decorative markings. However, because of its increased hardness, silica usually creates problems in processing. Bands of coarse crystals of calcite or dolomite are often present in marble. These bands may give the marble an uneven appearance and cause some difficulties in its processing. The conversion of sedimentary carbonate to crystalline marble takes place deep down in the earth’s crust, where high temperature and pressure are able to recrystallise the original carbonate. Although the primary structures of sedimentary carbonates, such as bedding, may be completely obliterated by metamorphic processes, colour and textural changes in marble may correspond to differences in the former depositional environments and in the products of the original sedimentary carbonates. This is particularly true for some marble varieties, such as marble breccias, marble interlayered with other metasedimentary rocks, grey and black marble, etc. The lithologic variation in marble deposits may also reflect diagenetic features of the former sedimentary carbonate rock, although metamorphic processes are the main factors responsible for the rearrangement of the lithofacies and their definitive arrangement in marble deposits. During metamorphism, marble undergoes intense ductile deformation produced by tectonic stress within deep shear and flowage areas of the earth’s crust. The most common structures that characterise most marble deposits are isoclinal folds, flowage folds, boudins, sheat folds, etc. Interference structures are also observed in marble deposits, when the region has undergone various phases of deformation. All these structures may be identified at all levels of observation. Silicate or other impurities usually mark the flowage structures and the schistosity that characterise marble deposits. Along the limbs of the folds, marble presents a linear arrangement of the internal structures, as these portions have undergone intense ductile stretching. As a result, bands of impurities are generally parallel to one other in fold limbs. Conversely, in the hinge area of the folds, marble is involved in minor drag or parasitic folds, that create a very wavy textural configuration of the bands of impurities. Marble deposits, as a whole, may have structurally complicated geometries as they originate from a complex deformation history, but exploitable marble bodies of a simple lenticular shape within other metamorphic rock types are frequently observed as well. 55

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Marble deposits occur in terrains of all metamorphic types along with other sedimentary-derived rock types. Static or thermal metamorphism may also generate marble whenever sedimentary carbonate has undergone heating by intrusion of large masses of magmatic rocks. Thermal metamorphism is indicated by the presence of accessory silicate minerals, such as tremolite and diopside. Fractures are commonly found in marble deposits. Fractures originate from the post-metamorphic fragile deformation of marble. Fracture systems are often regularly distributed in marble deposits and are related to the systematic stress distribution within the rock mass. Major fracture systems are often oriented parallel and perpendicular to the schistosity of marble, except in the hinge areas of the folds or whenever the schistosity of the marble creates complicated patterns on a large scale. If the spacing is sufficiently wide, these two major fracture systems are used for the removal of benches and blocks. In quarrying terminology, “grain” and “rift” indicate the two easiest splitting directions perpendicular to each other, which may coincide with the major fracture systems of the marble. Rock-bursts, which consist of sudden rigid expansion accompanied by fracturing of the rock, can often be seen along the wall surfaces of marble quarries. They result from the relaxation of the residual stress when the elastic limit of the rock is exceeded. The orientation of the principal components of residual stress determines the direction of the rock-bursts in marble. Residual stress in marble may result from the effect of tectonic stress or lithostatic loading, or a combination of both. Fractures induced by rock-bursts may develop horizontally or vertically, although they generally coincide with the easiest splitting directions or, rather, the major fracture systems of the marble. Seldom, residual stress release may cause the ductile deformation of marble that appears after a certain period of time after cutting into slabs. In the portions of rock near to the surface of many marble deposits, fracturing is more developed than deep down, and is characterised by close spacing and random distribution. Progressive residual stress relief causes this process as the stone load is removed by erosion and fracturing occurs near to the surface. The rock discontinuities near to the surface favour the development of sterile overburden, so that fracturing patterns, karst structures and weathering prevail over sound marble. The overburden may be several metres thick in marble deposits, and is particularly developed where flat topography or gently dipping slopes characterise the deposit area. In marble deposits dominated by steeply dipping slopes, the overburden is naturally removed by erosion. 56

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5.2 Granite deposits The commercial term granite refers to all magmatic rocks and some groups of metamorphic rocks that are characterised by a phanerocrystalline structure. The composition of dimension granite varieties ranges from acid to mafic, and includes all intermediate compositions. According to the commercial definition, true granite, syenite, monzonite, tonalite, all members of the gabbro series, anorthosite, piroxenite, and dolerite are all granites. The main constituent minerals of granite are: quartz, feldspar, mica, amphibole and pyroxene; olivine and feldspatoid occur only in most mafic compositions of commercial granites. Garnet, iron oxides, spinel and zircon may be present as accessories. Secondary minerals in granite are calcite, sericite, clay minerals and iron hydroxides. Due to the wide range of compositions, the commercial varieties of granite have different colours and textures. The colour of a variety of granite is determined by the dominant colour of some constituent minerals, and the overall rock shade may differ according to the proportion of these minerals within the rock. Coloured minerals are generally represented by feldspar, quartz and mafic minerals. The colours of feldspar ranges from white or light pink to dark red, including all the intermediate shades. Brown and green feldspars are also frequent (example: Baltic Brown – Finland). The blue colour of some granite varieties is given by the presence of sodalite, which is blue-purple (example: Azul Bahia – Brazil). Quartz, which is typically transparent, gives lighter shades or grey shades to the dominant colour of the granite. The relative abundance of mafic minerals gives dark shades to the colour of the granite. Some types of gabbro and dolerites, where mafic minerals are dominant, are regarded as black granite in current commercial terms (example: African Black, Belfast Absolut Black – South Africa, Zimbabwe Black – Zimbabwe). An iridescent colour is a distinctive colour of some varieties of anorthosite – labradorite (example: Labrador, Blue Pearl – Norway). The grain size of granite ranges from fine to coarse. Common structures of dimension granite are phanerocrystalline, and some are porphyritic. The texture of granite may be isotropic or oriented. In some gneiss and migmatites used as dimension stones, layers of light granitic material alternate with lenticular streaks or bands of a dark colour. This textural pattern may by regular and flat or highly contorted (example: Multicolor – Brazil, India, Africa). Colour uniformity, grain size and texture are critical requirements for granite used as dimension stone. Lack of uniformity rules out a great 57

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number of granite bodies from commercial use. In addition, isolated patches of mineral segregations, inclusions of country rock, altered portions of the rock, aplite, pegmatite and mafic rock dikes and knots are especially to be avoided. Commercial granites, except ignimbrite and metamorphites, are produced by the solidification of magma in deep portions of the Earth’s crust. Granite and granitoid rocks may be found in all geological provinces and ages, but their frequency and composition depends on the original geological setting. Although granite represents the main constituent rock of many basement areas of the world, granite compositions of the island-arc complex, continent to continent collision areas or continental rifting areas and anorogenic plutons differ from one other. A granite composition depends on the composition of the parental magma, the chemical-physical conditions of the area where the magma has progressively cooled and solidified and the processes of magma emplacement. The composition of granites varies according to the original geological environment and the evolution stage of the individual granite intrusion. The structure of the granitic bodies is determined by the mechanism of the emplacement of the liquid magma into the country rock before cooling as well as by later deformation history during and after the magma solidification. Regardless of the varying chemical composition, dimension granite deposits owe their common features to their structural grain. Granite may occur in the form of isolated plugs in an area of few square kilometres, or in large batholiths extending over tens or hundreds of kilometres. The term pluton is used to indicate all types of intrusive masses of different shape and composition. The overall structural configuration of plutons may be compared to that of diapirs, which may be simple or composite and range in size from tens to hundreds of kilometres. Concentration of inclusions and mineral segregations are also likely to be found more frequently near to the peripheral areas of the plutons than in the core. Pegmatite, aplite and quartz dikes may occur at the rim area of plutons as groups or swarms forming a radial or ring pattern, or both. Dikes may be also found isolated all across the plutons. The dikes range in thickness from a few millimetres to several metres, and their continuity may extend for a few metres up to several hundred metres. A continuous transition between metamorphites of high grade, migmatites and granites is a typical feature of many granitic basement provinces of the world. 58

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Deposits of migmatite and migmatitic granite are found in provinces where magmatic and metamorphic processes have both interacted and formed large areas of basement rocks. Gabbroic and mafic rocks have also been emplaced as plutons. Most gabbros and dolerites exploited as “black granite” are found as hypoabissal dikes or sills. These are frequently found in regions close to recent or ancient continental rifting, where magma of mafic and comparatively undifferentiated composition has risen into the upper crust. Fracturing is of great interest in quarrying dimension granite deposits, since it always represents the result of the brittle deformation of the rock. Fracturing of granite may be of primary origin, namely formed by the contraction of the rock during its solidification, or of secondary origin, if generated by stress after the complete solidification of the rock. Fracturing of primary origin is easier to recognise in hypoabyssal rocks, where cooling has been comparatively rapid. Some dolerite dikes have, for example, sets of columnar joints that develop perpendicular to the walls of the dike and form regular honeycomb-like hexagonal patterns. Rock portions limited by columnar joints range from a few centimetres to several metres long, and may be useful, when widely spaced, in the removal of blocks. Major fracturing systems in most granite deposits are represented by two major sets, along vertical planes or nearly so and at right angles to each other. These two orthogonal sets may have been produced by the brittle deformation of the rock as a consequence of tectonic stress. Alternatively, they may have been formed by lateral rock expansion as burial stress was relieved, or they may even be of primary origin. Intermediate, irregular and curved joints may also be found within the rock mass. If the orthogonal fracture sets are sufficiently and regularly spaced, rectangular benches or blocks may easily be removed and a quarry developed systematically. Fracturing which develops parallel to the bedrock surface, typical in flat topography, may also represent a very useful structural feature for the exploitation of many granite deposits. This type of fracturing pattern, if regular, may give rise to a “sheet structure”, since the granite is divided into sheets or tabular-shaped beds. The sheets range from a few centimetres to several metres thick and increase progressively, where sheets became more regular and flatter. The sheet structure seems to be developed independently from other fracturing systems or other rock heterogeneities. A tendency toward parallelism with the bedrock surface is observed in both hills and valleys. Whether the slope dip is gentle or steep, sheet structures are 59

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always found to be parallel or almost parallel to the bedrock surface. The origin of the sheet structure is attributed to the vertical expansion of the rock, due to burial stress relief as the rock load is gradually removed from the surface by the erosion. Massive granite with no internal linear or planar fabric or any other heterogeneity may have strong directional properties whenever rock parting is carried out. The rift is the easiest and the grain the second easiest direction for parting the rock. The two directions are commonly found perpendicular to each other in many granite deposits. In most granite deposits, one is vertical or nearly so and the other is horizontal or nearly so. The direction at right angles to the rift and the grain is called the Photo 17. Kenya: a boulder of black granite (by P. Primavori). hard way. The presence of rift and grain in granite deposits facilitates the removal of blocks of all sizes, from a few centimetres to bench sizes. Rift and grain are particularly evident in boulder quarries. Rift and grain do not necessarily coincide with mica plates or other minerals, whose alignment generates planes of rock that make for easy parting (i.e. rock schistosity, cleavage planes of Photo 18. Ghana: a veined granite quarry (by P. Primavori). feldspar, etc.). The origin of rift and grain in granite deposits may be regarded as the same as that of orthogonal fracture sets in granite, that are also found along vertical and horizontal planes. However, the presence of rift and grain may be related to mechanical anisotropies on a microscopic scale. 60

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Rift and grain are, in fact, thought to coincide with the main directions of pervasive micro-cracking of the granite mass formed during or after solidification. This micro-cracking extends into the feldspar and quartz grains and may develop independently from the orthogonal fracture sets. Micro-cracking may also occur along planes which are not necessarily parallel to the flowage structures often observed in many granite and migmatitic granite deposits. Morphologically speaking, granite deposits are found to have certain characteristics in common, regardless of differences in composition and structural framework. Morphologic features of areas dominated by the presence of granite are mainly determined by weathering processes and fracturing systems of the rock. The weathering of granite involves both chemical and mechanical processes and takes place gradually until the whole rock disintegrates. Chemical weathering of granite takes place by oxidation and other chemical processes in all climatic regions of the Earth. It produces progressive stages of degradation of granite. Staining represents the initial stage of chemical weathering processes of granite and is produced by the formation of iron hydroxides from the soluble iron content of the microscopic or sub-microscopic minerals within the granite. It is usually rusty-coloured and forms along fractures and micro-fractures, since they represent natural passageways for groundwater and hydrothermal fluids. Staining may be discontinuous, i.e. mainly developed along the fractures of the granite, or uniformly present throughout the rock mass from the surface down to several metres deep, if controlled by the presence of micro cracking. Stained rock is usually discarded because of the poor mechanical properties that usually characterise stained rocks. Some types of stained granites, however, if maintaining good mechanical properties, constitute a whole family of valuable dimension stones, commercially known as “yellow granite” (example: Giallo Veneziano – Brazil). Quarrying yellow granite implies the occurrence of uniform stained portions over extensive areas of the deposit. Stained granite is thought to be produced by the widespread hydrothermal alteration of the granite. Staining may affect large portions of the deposits and its distribution is not related to the morphology. It is, however, influenced by the micro-cracking pattern and the permeability of the granite that facilitates the spreading of staining. Further stages of weathering processes of granite lead to complete rock degradation until soil is formed. If weathering involves only the rock portions closest to the major fracturing systems and if these frac61

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turing systems are sufficiently spaced and developed along perpendicular or nearly perpendicular planes, a boulder topography is formed. Natural granitic boulders are usually rounded in shape, because weathering develops faster in the rock portions where fractures cross each other. Since weathered portions are mechanically removed by erosion, boulders stand on the surface as isolated or grouped remnants of unweathered granite. They are typical of many mature topography areas dominated by granite, and give origin to “stone mountains”. Boulders vary in size, depending on the spacing of the original fracturing pattern in a granite. Some boulders may even be in the region of thousands of cubic metres each. Conversely, weathering may develop uniformly from the surface downwards and may spread following the sheet structure of the granite. Flat or gently rolling topography is one of the most typical granite landform, and is found in mature topography areas where the sheet structure is particularly developed. This morphological feature occurs once the granite bedrock is completely uncovered by the erosion from its weathered overburden, which has developed parallel to the sheet structure of the granite. Flat or gently rolling topography is a typical morphological feature of many granite deposits, and sheet structures are generally exploited as the base of benches. Boulder and flat topographies may both occur in many granitic areas. Boulders are usually found near to the surface and may overlie a sound granite basement. Another typical morphologic feature of granite is a dome or “pan de azucar” topography. This occurs when granite is massive and emplaced as a fairly small isolated pluton surrounded by other rock types which are less resistant to erosion and weathering. Granite domes are characterised by marked sheet structures all along their surfaces. The presence of boulders rather than a flat topography in dimension granite deposits is determined by the dominance of vertical and orthogonal fracture sets over sheet structures. The dominance of either of these morphologic conditions will dictate boulder or bench quarrying, respectively.

5.3 Other dimension stone deposits In addition to carbonate rock (including sedimentary carbonate and true marble) and granite, dimension stone types include other rocks, which are also of significant economical importance. 62

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These include, besides metamorphic rocks (such as slate, micaschist, meta-sandstone, quartzite, serpentinite, ophicalcite), some types of volcanic or subvulcanic rocks (including basalt, tuff, porphyry, ignimbrite, trachyte) and sedimentary rocks, such as sandstone. Some of these dimension stone types are commercially known as marble, since they can be polished and their hardness is comparatively limited (serpentinite, ophicalcite). Other types, such as some porphyry ignimbrite and rhyolite, belong to the commercial category of granite, due to their higher hardness. Some other rock types, including slate, micaschist, volcanic rocks and sandstone, cannot be usually polished and are simply defined as stones. Some quartzite varieties can be polished. Nevertheless, regardless of the same degree of hardness as granite, due to the high silica content (more than 70%), quartzite is not considered as being a “granite” in trade language, because of its finer grain. The structural features of the deposits of these dimension stone types may differ substantially from those which characterise granite and carbonate rock deposits, and may dictate the adoption of special quarrying methods. Deposits of slate and micaschist (example: Verde Argento – Italy) have similar characteristics. Both these rock types are produced by more or less intense dynamic metamorphism, which involves close folding, recrystallisation and the development of pronounced rock cleavage, that usually develops parallel to the rock schistosity. The rock cleavage in slate and micaschist is used for splitting blocks or slabs without blasting. In serpentinite and ophicalcite deposits (examples: Verde Assoluto, Verde Antico, Verde Issogne, Rosso Levanto – Italy), although quarrying methods are similar to those used in marble deposits, the deposit geometry and fracture systems are in most cases peculiar to each individual deposit. Fracture spacing is crucial in exploiting serpentine and ophicalcite deposits, since massive portions of unweathered rock are rarely found in these deposits. However, due to the high market value of these rock types, many deposits of serpentinite and ophicalcite are exploited regardless of their waste/ore ratio, which is normally high. The large amounts of waste produced in these types of quarries are used by the crafts industry for the fabrication of novelties. Most deposits of basalt and other volcanic rocks are characterised by a tabular geometry and the presence of pronounced primary fracture systems, which are generated by the contraction of the rock during the late stages of its solidification. In quartzite deposits, regardless of the effects of metamorphism, which are responsible for the extensive recrystallisation of the origi63

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nal arenaceous rock, remnants of primary structures, such as bedding, oriented fabric, ripple marks, etc., may be well preserved. Structural features of quartzite deposits may be comparable to those which characterise some sandstone deposits. The reconstruction of original depositional environments of quartzite may be an useful tool to predict a rock’s uniformity and estimate its reserves. Fracture systems in quartzite are determined by the brittle deformation of beds. The presence of major structures, such as large scale folds, regulates the fracturing arrangement of the quartzite. Fracture sets are generally closely spaced in quartzite deposits and, as a consequence, a high waste/ore ratio characterises most dimension quartzite production.

5.4 Location of the dimension stone deposits Dimension stone deposits are found in all countries and all geological environments in the world. Rock type, extension and area distribution of exploitable dimension stone are however influenced by the geological setting where exploitable dimension stone is found. Each geological setting is characterised by the presence of particular rock series and groups, which vary from one region to another. Generally, only a small number of rock types have a real potential as dimension stones, and only small portions of any interesting rock formation can be exploited for dimension stone production. Stable cratonic areas are dominated by granitoid and metamorphic rocks, including granite, granitoid rocks, slate and marble, which may be intruded by anorogenic plutons of varying composition (anorthosite, gabbro, ultramafic rocks, etc.). In cratonic areas, all geological environments and relative rock assemblages may be found as remnants of various ancient (Precambrian) orogenetic events that have generated complex tectonic interferences and overprinting phenomena. For this reason, the correlation of rocks belonging to cratonic areas which were moved apart during the Phanerozoic age may be of little significance. Dike swarms may occur in formerly active or aborted continental rifting areas, forming important sources of “black granite” (dolerite, gabbro, etc.) within cratonic areas. Undisturbed or slightly deformed sedimentary rocks covering stable basement areas may constitute important sources of sedimentary dimension stone types. Continent-to-continent and continent-to-ocean collision areas may represent excellent sources of all kinds of dimension stone, even in highly tectonised areas. 64

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Alpine-type collision belts are endowed with a large variety of valuable dimension stones, including granite, granitoid rocks, serpentinite, marble, slate and limestone. Cordilleras and island arc ranges may be particularly interesting for some rock types, such as serpentinite, gabbro, diorite, granodiorite, true marble. Sedimentary carbonate deposits may occur in uplifted basins, where carbonate platform sequences were deposited which have resisted later erosion and weathering. Exploited or potentially exploitable dimension stone deposits are often found in restricted areas, such as thrusted sheet and amalgamated terranes, the characteristics of which cannot be easily connected with those of the general geological setting where these areas are found. The present geographic distribution of major dimension stone production areas is not only determined by the favourable geological conditions of these countries. The historical background of the dimension stone industry, the economic development and the political conditions of the producer countries still represent the most significant factors for the geographical distribution of dimension stone exploitations. The global distribution of dimension stone deposits does not necessarily match the actual location of potential areas, due to the lack of specific inventory data on dimension stone resources in many countries of the world. In addition, the exploitation of dimension stone deposits is governed by the logistics, the vicinity to the market and the economic development of the country where these deposits are located (see chapter 7).

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Quarrying methods and technologies

6. Dimension stone quarrying 6.1 Quarry products The basic goal of all dimension stone quarrying operations is to optimise the production of stone blocks or units properly dimensioned for direct sale or further processing. Form and dimensions of stone units vary according to the stone end use and are regulated by selling prerequisites. For architectural uses of stone, which is the most important use in the stone market, sized blocks suitable for industrial processing are required. In addition to stone quality consistency (i.e. lack of defects such as colour variation, textural changes, inclusions, fractures, etc.), the industrial standard for processing stones used in architecture requires that stone blocks are of regular rectangular shape. The maximum length and height of the blocks are constrained by the dimensions of the gang-saw frame, where blocks are placed and cut to produce slabs. Block dimensions range between 2.8 to 3.2 meters in length, and between 1.5 to 1.8 meters in height. The block maximum width is constrained by weight limits that are given by safety factors in handling and transportation of the blocks. Quarrying and processing practices demonstrate that the larger block dimensions are, the lower their production costs and the higher the processing yield. In addition, the larger the surfaces of finished products (slabs), the higher the price of end products. The dimensions of specific end products, such as architectural panels for cladding surfaces of buildings, dictate the block dimensions. For instance, panels of 60 x 60 x 2 cm are obtained with a good processing yield if block dimensions are multiple of 60 cm, net of off-cuts. In order to maintain the processing yield within acceptable tolerance limits, the form of blocks should be as regular as possible, roughness of block sides the lowest, and parallelism between opposite block sides consistent.

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The commercial volume of blocks is computed according to the dimensions of the maximum rectangular prism inscribed into the actual block volume, minus an allowance of 5 cm per side, which corresponds to the processing off-cut portions of the block. The total off-cut volume decreases as form regularity of blocks increases. Aesthetic characteristics that appear in finished stone surfaces change in relation to the orientation of block-cut-direction. This depends on the texture of the stone, if stone has an oriented texture at all (Figure 2). Mechanical properties of finished stone products are also influenced by orientation of block-cut-direction if stone has strong directional properties. If the stone is used for the production of tiles, block sizes may be smaller than those of standard blocks used for the production of large slabs. Form regularity of blocks is not a special requisite for production of tiles. Ashlar, flagstone, rubble stone, novelties, terrazzo-aggregates may be produced from the quarrying waste and finishing off-cuts. In most cases, dimension stone quarrying is profitable, if production of sizeable blocks and regular shape is carried out with a comparatively high recovered blocks-to-waste ratio (or recovery percentage of blocks). Small blocks and blocks of irregular form may be recovered as quarrying by-products, as their commercial value is comparatively low when compared to that of sizeable blocks. The recent market growth of tiles has encouraged the restoration of many quarries, where blocks of comparatively small sizes, but with uniform lithological characteristics, represent the bulk of production.

6.2 Quarrying configuration The arrangement and the geometrical configuration of dimension stone quarries depend on the type of exploited dimension stone, quarrying methods, morphologic characteristics, size, as well as the geometry and structural features of the exploitable body. The type of dimension stone alone does not determine the quarry configuration. In fact, similar quarrying methods may be applied to different types of dimension stone quarrying. Morphological conditions and structural and geometrical features of the deposit dictate quarrying methods, planning and geometrical configuration of the quarry. Many dimension stone deposits are suitable for a boulder quarrying method. Boulder quarry may represent the initial stage of a quarry development, wherever the overburden of the deposit is represented 68

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Figure 2. Possible panel arrangements (by Masonry Institute of America, 1989 – modified).

by exploitable boulders. If the total reserves of the dimension stone deposit are represented by boulders, boulder quarrying may persist for the whole duration of the quarry life. 69

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Boulder quarries, ordinarily developed in dominant flat topographies or along gently dipping slopes, lack a regular geometry. Many granite and carbonate deposits are affected by intense weathering, which is a typical feature of many tropical regions. This makes them suitable for developing into boulder quarries. Bench quarries are generally considered to be preferable for dimension stone exploitation, since they allow a regular and checkable quarry development. Boulder and bench quarries represent two extremes of a large number of quarrying methods (Figure 3). As in most dimension stone quarries, quarrying blocks is carried out taking advantage of the presence of regular fracturing patterns or pronounced directional properties of the stone, that dictate the quarry development and geometry. Bench quarries may assume different shapes and configurations, depending on the morphologic and structural characteristics of the deposit. Quarrying always follows the geometry of the exploitable rock mass that may occur in the form of beds, layers, or other complex geometrical configurations. Bench quarries of dimension stones are developed as openpit operations, whereas underground dimension stone quarPhoto 19. Granite block of commercial size (by P. Blasi) ries are still a minority. Underground quarries are developed wherever it is the only way to exploit the deposit. Landscape preservation can also represent an important constraint for the underground development of dimension stone deposits. The underground quarrying of a dimension stone can be executed safely and in a technically viable manner only when there is an high grade of rock integrity. Photo 20. Marble slab of commercial size (by P. Blasi). Underground dimension 70

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Figure 3. Initial development stages in a small scale quarry operation (a: marble quarry; b: granite boulder quarry). (by G. Milazzo)

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stone quarries are represented by room-and-pillar quarries. Quarrying methods used in open pit and underground dimension stone quarries are similar to each other, both involving progressive downward lowering of the quarry floor by removal and levelling of benches. Open pit quarries of dimension stones are on average characterised by steeply dipping or near to vertical pit slopes, as the comparatively high rock soundness of most dimension stone deposits does not generate problems of slope stability. In regions where the topographic surface is flat and gentle, open pit quarries may assume a typical configuration similar to that of an amphitheatre, with several quarry fronts and beds, where the various phases of the operation may be done simultaneously. If the pit bottom is below the water table, pumping plants and channelling systems need to be set up in order to keep the working areas dry. When open pit quarries are developed along hills or mountain sides, the shape is similar to that of a portion of an amphitheatre. In such cases, water is easily removed from the excavation area by simple drainage systems or captured and re-cycled to feed the quarrying equipment. Construction and maintenance of quarry roads is a major concern of hill or mountain side quarries. Areas that are abandoned and dump areas can be re-used for the construction of quarry roads for such types of quarry. If quarries are located on hill or mountain tops, the development proceeds by progressively removing the top and then gradually lowering and levelling the rocky surface.

6.3 Quarrying sequence Dimension stone quarrying operations basically involve isolating blocks from the parent ledge by cutting it free on all sides perpendicular to each other. The isolated stone block has dimensions suitable for sale and processing. It may be much larger and further subdivision into smaller blocks may be made. Quarrying operations vary from a quarry to another, depending on all factors previously mentioned. The basic quarrying sequence includes the following working steps: – pre-production operations; – primary cuts; – secondary cuts and finishing of blocks; – removal and haulage of blocks. The production efficiency of the operation increases if these four working phases may be done simultaneously. This sequence represents the guideline for a correct work organisation in the quarry. 72

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6.3.1 Pre-production operations Preparation to quarrying includes development of infrastructures, i.e. quarry roads, quarry yards, preparation of dump areas, installation of facilities and ancillary services, and opening of the quarry. To guarantee efficient and safe operational conditions, the width of quarry roads should not be less than 5 meters and the slope of quarry roads should not exceed approximately 20%. The quarry roads and any other embankment or artificial slope prepared for the quarry must be kept in good conditions and maintained by a properly designed and arranged drainage system. Quarry yards are large enough to comply with the manoeuvrability requirements of the quarry equipment. Dump areas are conveniently located in areas that will not cause interference with excavation and haulage activities. Slope stability, drainage system, volume and dimensions of the production waste, are all components of the dump areas to be considered in order to minimise risk of rock falls and to limit the negative environmental impact that dump areas always produce. Installation of all utilities and all those infrastructures which are necessary to serve quarrying operations, such as water supply, electrical power, fuel reservoirs, warehouse, repair shop, is also done at this stage. Removal of overburden may be done by means of scrapers or bulldozers. A working trench or channel is then made on the quarry floor or on the mountainside to provide a large enough working space on vertical rocky walls, that are prepared in a manner to maintain parallelism to the desired direction of excavation. Such a trench or channel may be made by conventional mining methods (i.e. blasting and mucking) or by drilling two rows of parallel core holes and removing the rock between them after broaching or blasting. Channelling consists in making a narrow vertical cut of planar trend into the rock by means of drilling holes and subsequent blasting or using natural fracture planes. Channels should be made parallel or perpendicular to the direction of the future primary cuts of the quarry. Channelling by jet piercing or by diamond wire cutting may be used in granite quarries (see next paragraph). In the most favourable morphologic and structural conditions of the deposit, opening procedures may be similar to removing blocks in an open quarry with no need of trenching or channelling. In marble deposits, opening procedures may be similar to removing blocks, when the combining methods of chain saw or diamond belt saw for vertical cuts, and diamond wire saw for horizontal cuts, are used. Obviously, in this first phase of operation, the block recovery percentage may be very low when compared to the quarry development at its optimum stage. 73

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6.3.2 Primary cuts Primary cuts are made in order to separate benches or big rock slices from the parent ledge. Bench sides are planar and perpendicular to each other. They are commonly horizontal and vertical. The sides of the benches are maintained orthogonal to each other when the base lifting plane of the benches coincides with the inclined bedding surface or sheeted structures. Benches may be up to tens of meters in length, whereas their width and height is constrained by multiples of block dimensions plus additional allowances due to eventual off-cut volumes. Bench length is parallel to the direction of excavation of the quarry, that is selected in consideration of the directional properties of the stone, attitude of main fracture systems and direction of the planar texture of the rock (sedimentary layering, schistosity, flowage structure, etc.). Bench width has to be equal to or smaller than its height to facilitate bench overturning after detachment from the ledge. 6.3.3 Secondary cuts and removal of blocks Numerous rock slices may be obtained from a single bench. These are usually cut perpendicular to the bench length and are hence turned over onto the quarry yard. Slices are subdivided by secondary cuts into blocks of commercial sizes. If bench width is equal to block width plus additional off-cut dimension allowances, blocks are cut directly from the bench, once the bench is turned over onto the quarry yard. Blocks are removed directly from the ledge when the spacing of bedding or other rock discontinuities is regular and corresponds approximately to the block dimensions. Once given a final squaring to the blocks, if necessary, these are transported to the stock yard or sent directly to the processing plant.

6.4 Quarrying technologies Separation of benches, slices and blocks from their parent ledges may be done by using natural joint surfaces. Failing these, cutting requires the use of mechanical tools. The most frequently used stone cutting technologies may be grouped into three main categories: – cutting by drilling; – cutting by abrasion; – cutting by disaggregation.

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6.4.1 Cutting by drilling This technique is normally used wherever exploited stone is characterised by a comparatively high hardness and abrasion coefficient, such as most granite, quartzite and other siliceous rocks (Figure 4). In addition, cutting by drilling is done in all those deposits where water supplying, which is essential to cutting by abrasion, is not viable. In quarries where the preferred cutting method is by abrasion, drilling methods still represent a valid support (Figure 5). Drill holes may vary in length, depending on the depth of the cutting surface. Drill depth may be from 3 to 9 meters in primary cuttings, i.e. in bench or slice separation, or from 1.5 to 3 meters when block cutting is performed. The hole diameter corresponds to the diameter of the drill rod series which normally varies from 32 to 36 mm; drill bars series of 40 or 42 mm are also used. Cutting by drilling may be performed following two major procedures: – channelling by line drilling: drill holes are in the same plane, parallel to each other, closely spaced and intersected one to another, so as to make a channel cut; – line drilling and pre-splitting: drill holes are in the same plane, parallel to each other, and drilled at a regular distance, which may vary from one cut to another from a few centimetres up to 25 cm, with an average of 15 cm. Then, rock separation is done by presplitting or soft blasting (Figure 6). Channelling is comparatively common in granite quarries, but only along some particular cutting planes, such as the opening of channels, where the use of pre-splitting would affect the rock integrity. Generally speaking, an extensive channel cutting in granite is not economically viable because, due to the relative hardness of this material and the large amount of drill holes to be made, it would involve a high consumption and frequent sharpening of drill rods. The combination of drilling and pre-splitting is the most popular cutting method used in granite quarries, but it is also commonly done in marble or limestone quarries, where cutting by abrasion methods are not applicable. Pre-splitting consists in firing light linear charges inserted into the holes. The most common explosive charge which is normally used is the detonating penta-erythrite fuse (8 to 12 g PNT/m). Alternative explosive types are also used, such as the mixture of ANFO explosive with ammonium nitrate and fuel oil in fixed proportions, and black powder. All strands of detonating fuse are inserted into the holes and connected to a master cord, so that firing occurs almost simultaneously.

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Figure 4. Granite quarry layout, with “sheet structure” parallel to the slope; channelling by diamond wire saw, cutting by in-line drilling, controlled blasting and/or wedging (by G. Milazzo)

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Figure 5. Example of marble quarry layout, showing the simultaneous use of chain saw or diamond belt saw, diamond wire saw, drilling units and expansion bags (by G. Milazzo)

Figure 6. Medium-large scale granite quarry development outlook; all cuts are done by in-drilling, controlled blasting or wedging (by G. Milazzo)

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Photo 21. Granite quarrying: combination of cutting by drilling and abrasion (by M. Gomez).

Photo 22. Granite cutting by diamond wire (by P. Blasi).

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The charge-hole wall gap may be filled with water if a more powerful explosive effect is desired in rock pre-splitting. This is normally done in granite quarries. There are some major differences and prerequisites in the pre-splitting methods of dimension stone quarrying with respect to those used in ordinary mining operations: – the linear charge is much lower than in conventional pre-splitting; – the rock integrity of the separated masses has to be maintained after pre-splitting: radial cracks that develop around the holes must be avoided or reduced; – a controlled amount of displacement of the detached rock mass from the parent ledge is desired. Theories that have been developed to explain the pre-splitting mechanism converge into two main categories: • superposition of shock waves from adjacent holes; • generation of tensile stress conditions, which produce a master crack connecting the holes. Much practical and experimental work is currently done with the aim of optimising the charge consumption in dimension stone pre-splitting techniques. One tentative formula that relates specific consumption of charge with stone production is the following:

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PF = A + B * S/V + CxS where PF is the specific consumption (g/m3), S the cut surface (m2), V the exploited volume (m3), S the displacement (m), and A, B, and C are empirical coefficients with the respective dimensions of g/m3, g/m2, and g/m4. Another empirically determined formula correlating rock mechanical properties, charge and drill hole characteristics is the following: (dc/df)2 x (lc/lf) x De x Kw x ps x [df/(E - d1)] = K1 x ts where df is the drill hole diameter (m); dc is the charge diameter of the detonating fuse (m); dc/df is called decoupling parameter; lf is the drill hole length (m); lc is the charge length inserted into the drill hole (m); De is the charge relative density into the detonating fuse (1.3); ps is the specific pressure of the charge (about 1200 MPa); E is the reciprocal distance of the drill holes (m), K1 is an empirically determined coefficient equal to 0.5; Kw is a coefficient which is equal to 2 if the holes are filled with water and ts is the tensile strength of the rock. In order to reach the maximum efficiency of pre-splitting, all the variable parameters included in the above reported formula should be considered and their optimisation should be empirically pre-determined at the initial stages of quarrying both by practising and modelling. There are also some equations used in computing the shortest tolerable distance from the pre-splitting site to buildings because of seismic vibrations induced by the firing charges. Pre-splitting may be done simultaneously along the base and sides of benches (slices or blocks). Normally, base detachment or lifting by pre-splitting requires a relative larger amount of charge per cut unit area, with respect to that used in lateral pre-splitting. In fact, in addition to the energy required for the detachment, more energy is required for lifting, because of the weight of the detached rock portion. Stone cutting by pre-splitting should be done parallel to the easiest directions of rock breaking and taking advantage of natural joint planes, if any. Indeed, if the main directions of tensile stress induced by charge firing in pre-splitting coincide with those of rock residual stress, presplitting may be performed with maximum efficiency. On the contrary, where parallelism between cutting planes and easiest rock breaking directions is not observed, the rock integrity may be affected by the formation of visible or even invisible cracks, which develop near the cut surface and increase off-cut volumes.

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For this reason, one of the most important prerequisites of pre-splitting by soft blasting is the understanding of the rock mechanical behaviour. Fracturing analysis and exploratory excavation may help. Black powder is another type of explosive charge being successfully used in pre-splitting. The use of black powder is particularly suitable in all those cases where rock easiest parting directions are well defined, such as in many granite boulder quarries, i.e. in all those types of deposits where residual stress conditions are comparatively homogeneous and residual stress magnitude is near to exceed the elastic limit of the rock. In such cases, spectacular and high-efficiency vertical cuttings of stone may be obtained by simply blasting from a single and short vertical drill hole, which has been partially filled with black powder. Sometimes, this is called the “block-hole” method. Black powder is also used when the rock portion to be cut is already detached from its ledge by natural joints and when further separation or lateral displacement of the exploiting rock mass is desired. 6.4.1.1 Drilling equipment Cutting by drilling in dimension stone deposits is normally done by means of pneumatic or, in fewer cases, hydraulic drilling tools. This drilling equipment is: a) jack-hammers; b) drill rigs; c) wagon drills. a) Jack-hammers Jack hammers operated by compressed air are of different sizes and accordingly used for different cut types. Manually held jack-hammers are from 10 to 15 kg in weight and are normally used in secondary cuts, whereas heavy duty jack-hammers are mounted on a quarry bar, such as in block-cutters, or built in a rigid frame (wagon drill). Their air consumption is approximately: – 1400 l/min for 10-13 kg jack-hammers; – 1800 l/min for 15-16 kg jack-hammers; – 2500 l/min for 23 kg jack-hammers. There are also some hydraulically operated types. Hydraulic jackhammers are renowned for their longer life and lower maintenance costs than normal pneumatic jack-hammers, but their cost is much higher. All types of jack-hammers are operated by means of a percussion and rotation mechanical device, so that simultaneous percussion and rotation movements are conveyed to the drill bars which are inserted into the terminal inlet of the jack-hammer.

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Photo 23. Pre-splitting phases in a granite quarry (a, b: by P. Blasi; c: by IMM Archive).

Drilling progresses by simultaneous chiselling and chopping actions exerted by the drill bars against the rock. The percussion-rotation frequency varies from 1500 up to 3000 shots per minute. The chisels are made of tungsten-carbide and are periodically sharpened. The chisel consumption rate depends on the rock type being drilled and on the power of the jack-hammer, i.e. percussion-rotation frequency and propelling force or push transmitted to the chisel. This push should correspond to approximately 50 kg in the lightest

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types of jack-hammers and may reach up to 250-300 kg in heavy-duty jack-hammers. For each rock type, the drilling efficiency of the jack-hammer is maximised when the most suitable coupling of percussion-rotation frequency and push is reached. In addition, wrong power conditions in drilling operation, i.e. either undercharged or overcharged compressed air or push transmitted to drill bars, may cause rapid damages to both jack-hammers and drill bars. The axial portion of drill bars has to be empty up to the terminal chisel, to allow compressed air to circulate inside the drill bar and keep the drill hole constantly clean from rock fragments and powder produced during drilling. The drill bar life may reach 150-200 meters of drilling length in most abrasive rock types, such as granite, quartzite, etc., whereas it is much longer in marble and limestone. b) Drill rigs One of the most common drilling tools, which is particularly used in granite quarries, is the drill rig. It consists of one up to a maximum of four heavy duty jack-hammers (most commonly two jack hammers) mounted on a rigid frame, which can be easily anchored on the quarry floor or on the rock portion to be cut. This frame may be easily unanchored once cutting is finished. The quarry bar holds the heavy-duty jack-hammers rigidly in position. Constant thrust force, which is appropriate to the power of the jackhammers, is provided during drilling by a pneumatic hold device. The jack-hammers can slide back and forth along the quarry bar by maintaining constant parallelism, so that the row of holes being drilled comes out aligned and on the same plane. Drill rig allows cutting to be done in all desired orientations, as jackhammers can be turned from 0° to 90° with respect to the rigid frame. Drill rig yields a drilling efficiency much higher than that obtained using manually held jack-hammers. Parallelism between holes, drilling speed and number of workers (only one or two) are further advantages of drill rigs against manually held jack-hammers. c) Wagon-drill The wagon-drill is a drilling tool composed by a quarry bar where two or more (maximum four) heavy-duty jack-hammers are mounted, as in the block-cutter. The quarry bar is mounted on a wheel or chain tractor. The quarry bar and the jack-hammers may be hydraulically posi-

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tioned, and drilling may be done accordingly. The wagon-drill is used in large scale operations as the high cost of this tool cannot easily be afforded by average-sized companies. 6.4.1.2 Wedging Rock splitting in secondary or minor cuts may be conveniently done by wedging. This technique requires the use of mechanical tools instead of explosive charges, which may cause damages to the rock when the latter is particularly fragile. The wedging tools are manual, such as plugs and feathers, or powered, for instance hydraulic feathers. The depth of inserting feathers and plugs into the drill holes as well as their reciprocal distance vary depending on the rock type, block size and extension of the cut surface. Rock separation may also be carried out using expansible fluids, which are poured into the drill holes. Expansion occurs when the fluid dries up and causes the rock to part along the surface between the holes. 6.4.2 Cutting by abrasion Cutting stone by abrasion is a particularly suitable technique for all rock types of comparatively low hardness, such as carbonate and serpentinite, but its application to granite is now spreading. One advantage of cutting stone by abrasion, instead of drilling, is that it produces lower amounts of waste and preserves rock integrity. Blocks with smooth and regular sides are produced with cutting by abrasion methods, so that the volumes of offcuts are minimised during finishing. Cutting by abrasion techniques include: – helicoidal wire saw; – diamond wire saw; – chain saw; – diamond belt saw; – disk cutter. Photo 24. Wagon-drill in a limestone quarry (by P. Blasi).

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Photo 25. Drill-rig in a sandstone quarry (by P. Blasi).

6.4.2.1 Helicoidal wire saw The helicoidal wire was the most popular technique for cutting marble in the past. Nowadays, it has been replaced by more simple and efficient cutting methods. The helicoidal wire consists of a double or triple strand of wire that runs over sheaves and is fed under tension into the stone. The wire feeds a constant flow of silica sand (alternatively, aluminium oxide or some other kind of abrasive) and water and wears a groove or channel in the stone. The sheaves are mounted on a tower or track, so that they can be moved into the cut. In order to press the wire into the cut, the block or stone being cut must show two free and parallel sides or else a large hole to let in the sheaves. In some cases, the hole needs to be just large enough to let in the axle, hub and the supporting arm of the sheave. The sheave is designed to cut its own groove as it is pressed into the stone. In some operations, other cutting methods are used to cut parallel channels between which the stone is wire sawed. The wire used may be thousands of meters long, and a single wire may be used to make several cuts simultaneously by guiding it with an appropriate arrangement of the sheaves. An electrical engine drives the wire through a guide sheave. The wire runs at a speed of 5 to 10 m/s. The cutting speed by using helical wire saws in true marble is 0.5 to 1.0 m2/hour if silica sand is used, and may reach more than 2 m2/hour when aluminium oxide is used as an abrasive. 84

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At least one movable sheave must be set up in the wire circuit with appropriate counterweights in order to keep the wire properly stretched. Helicoidal wire sawing is still preferred to other more modern quarry cutting methods in some stone quarries, where particular conditions for performing very large primary cuts make this method viable. 6.4.2.2 Diamond wire saw Since the seventies, diamond wire saws have progressively replaced the use of wire saws and are now the most common method for cutting marble. Diamond wire saws consist of a multi-strand steel wire of 4-5 mm in diameter, along which numerous diamond coated or impregnated beads positioned at close and regular distance between each other. The diameter of the diamond beads is a few millimetres wider than the wire diameter, so that abrasion is exerted by the diamond beads only during stone cutting. The space between the diamond beads is occupied by spring or plastic cylinders, which protect the wire without changing its flexibility. Diamond coated or electroplated beads are used to cut comparatively soft stone types, such as chalky limestone and marble of low cohesiveness, whereas impregnated or sintered diamond beads are mostly used to cut a wide Photo 26. Helicoidal wire saw in a travertine quarry (by P. Blasi). range of stone types, which vary in abrasiveness from low (marble, limestone) to high (granite, sandstone). The cutting speed of sintered diamond beads is lower than that of electroplated ones, but their durability is generally much longer. In order to maximise the performance of diamond wire cutting, different specific types of sintered diamond beads may be used which should be selected Photo 27. Drill rod sharpener (by P. Blasi). depending on hardness, grain 85

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size and interlocking of the main minerals forming the stone to be cut. In each type of sintered diamond bead, the grain size of the diamond grit and the proportion between diamond grit and metal bond may significantly vary; usually a copper-nickel or cadmium alloy is used as a metal bond for sintered diamond beads. The diamond wire is driven by a flywheel operated directly by an electric motor or through a mechanical driving device. The tensioning control of the diamond wire can be of different types, according to the brands of diamond wire saws; a smooth and selfadjusting control of the tensioning system has to be preferred among others, as it maximises the performances (cutting speed and life) of the diamond wire. This is a very important factor to be considered for the economy of the quarry operation, as the diamond wire represents one of the most expensive consumable items in many quarries. Stone cutting by diamond wire saws is made possible by setting up the wire as a loop around the rock portion to be cut (Figure 7). The loop is initially set up by drilling two converging holes which define the limits of the cut surface. The maximum extension of the cut surface is limited by the maximum length of these converging holes, which correspond to 8-12 meters each. The loop initial length is up to 50 meters or more than that and is progressively reduced during step by step backward movements of the machine. The backward movement of the machine as the cut progresses occurs along rails which are anchored to the ground. The wire needs constant feeding of water for cooling and keeping the wire clean from rock slime during cutting. The water consumption in diamond wire cutting is approximately 1 l/m2/min. The continuous development in diamond wire saw technology includes efforts to improve the quality and cutting performances of the diamond beads and the effectiveness of diamond wire machines. This has resulted in a large number of models of diamond wire saws, which are suitable for different types of stone to be cut, including granite (Figure 8). The advantage of using diamond wire saws for stone cutting rather than helicoidal wire is demonstrated by: – reduced manpower (2-3 workers only); – increase of cutting speed (up to 10-12 m2/hour in true marble); – easy installation. Cuts may be done horizontally or vertically by positioning the loop and the engine-stretching-flywheel tool accordingly. Diamond wire saws may be used in sizing blocks into regular shape before processing. In such a case, a special diamond wire tool has been designed for this particular purpose. 86

Figure 7. Work layout in a marble quarry, showing a chain saw or a diamond belt saw combined with diamond wire cutting (by G. Milazzo)

Figure 8. Work layout in a granite quarry, showing the operational sequence: primary cutting by diamond wire; secondary cutting by in-line drilling-wedging; block cutting by in-line drilling-wedging (by G. Milazzo)

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6.4.2.3 Chain saw The use of chain saws is limited to cutting marble, non-metamorphic carbonate, serpentinite and ophicalcite. The chain is provided with tungsten carbide teeth. Generally, the chain saw arm is designed to achieve a useful cutting depth of 3 meters. The chain propeller is an hydraulic engine, which is in turn propelled by an electric motor of about 45 kW. Chain speed may reach 7 to 8 meters per second, but is reduced to 23 meters per second in most marble quarries. Cutting is performed by pushing the whole arm of the chain saw though the rock in a perpendicular position with respect to the moving direction of the machine. During cutting, the chain saw moves hydraulically along fixed and rigid metallic rails or along a cylindrical bar. The latter is used in underground operations. Water is injected into the cut surface during cutting, for cooling purposes. The amount of required water is from 1 to 1.2 litres per second. Rotation and change of the tungsten carbide teeth involve several stops during chain sawing operations. Chain sawing can also be performed in dry conditions, but in this case a reduction in the chain speed and an increase in the torque of the drive gear of the chain are both needed (Figure 9). The cutting speed of the chain saw is about 5-6 square meters per hour in marble. Chain saws are designed for performing both horizontal and vertical cuts. This tool is frequently employed in underground and open-pit quarries, where large and flat surfaces of solid marble may be prepared to let the chain cutter move smoothly along the rails. Due to its comparatively heavy weight (5-7 tons), the chain cutter requires the use of mechanical lifting tools during each installation. Chain cutters and diamond wire saws may be used jointly: the former for horizontal cuts and the latter for primary vertical cuts. This is possible whenever quarrying methods contemplate the exploitation of high and narrow benches and in pit quarries (Figure 10). 6.4.2.4 Diamond belt saw This is a new technology for stone cutting that can be applied to any stone type, including all hard and abrasive sandstone varieties, with the exception of granite. Although the diamond belt saw is structurally comparable to the chain saw, the cutting mechanisms are totally different. The diamond belt saw has a plastic belt with impregnated diamond segments placed at regular intervals, while the chain cutter has a chain with the tungsten carbide teeth inserted. Equipped with a 50-55 kW electric engine, the diamond belt saw has a device for automatically regulating the cutting speed of the belt as a func88

Figure 9. Work layout in a fractured limestone quarry with horizontal bending in dry conditions; vertical cutting is done by chain saw or in-line drilling; horizontal surfaces correspond to the bedding plane.Work layout in a granite quarry, showing the operational sequence: primary cutting by diamond wire; secondary cutting by in-line drilling-wedging; block cutting by inline drilling-wedging (by G. Milazzo)

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Photo 28. Diamond wire saw (with belt protection, in the top picture) (a: by P. Blasi; b: by IMM Archive).

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tion of the resistance of the rock to be cut. The diamond belt does not require oil or grease lubrication, but water consumption is higher than in chain saws (2-3 litres per second), since the belt speed is higher than the chain speed in the chain saw. A large amount of water is needed in diamond belt sawing to keep the diamond tools clean and cool, and to allow the belt to glide on its guide bar through a water cushion (“aquaplaning”). The cutting speed of the diamond belt saw is 4-5 m2 per hour in marble. The weight of the machine is about 5.5 tons. The use of the diamond belt saw is widespread, including carbonate rocks, marble, limestone, serpentinite, slate and sandstone. Moreover, inclusions of abrasive materials, such as quartz veins or nod-

Photo 29. Preparation of the diamond wire loop (by P. Blasi).

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Figure 10. Chain saw or diamond belt saw used in conjunction with diamond wire saw in a marble quarry, with no need of making two converging holes, wherein to thread the diamond wire (by G. Milazzo)

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ules found in many marble types ever so often, are cut more easily with a diamond belt saw than with a chain saw, as the tungsten carbide teeth of the chain would be seriously damaged by the abrasive material encountered during the cutting. The operational cost of the diamond belt saw mainly depends on the type of material to be cut, but is comparable to that of the chain saw.