Northern Virginia Community College Alexandria, Virginia Dr. Victor P. Zabielski
GOL 105: Mineral Identification Lab Objective: Minerals are the basic building blocks of all rocks. The identification of minerals is one of the most basic skills in geology. Although there are over 4000 different minerals, a working knowledge of 10 – 20 of them will allow you to identify most rocks by their composition. The objective of this lab is to introduce you to the diagnostic properties of minerals and acquaint you with several of the most common minerals that you will encounter in most rock types.
Part I: Diagnostic Properties Provide brief descriptions for each of the following diagnostic properties of minerals. For each property, give an expected range of values (for example, transparency can range from transparent to translucent to opaque). You will use these properties to help you identify the mineral specimens in this lab. Definitions for each of these properties can be found in your Laboratory Manual in Physical Geology (Laboratory 3, p. 37) and in your textbook Essentials of Geology, (Chapter 3, section 3.4, p. 87).
Habit (or Shape) Definition:
Examples/Range:
Cleavage Definition:
Examples/Range:
Fracture Definition:
Examples/Range:
Hardness Definition:
Examples/Range:
Specific Gravity Definition:
Examples/Range:
Color Definition:
Examples/Range:
Streak Definition:
Examples/Range:
Clarity / Transparency (light penetration) Definition:
Examples/Range:
Luster (light reflection) Definition:
Examples/Range:
Accesory properties (texture, magnetism, etc..) Definition:
Examples/Range:
Part II: Mineral Identification This exercise is meant to get you to learn how to identify minerals using the properties that you described in part I of this lab. First, list the properties of each of the minerals in the accompanying Mineral Identification Charts provided. Some properties will be more easily determined than others. Second, use the flow charts at the end of this lab to help you identify each of the minerals. The flow charts are designed to allow you to use the most basic and simplest properties to first identify the mineral (color and cleavage) and then to further narrow down the minerals identity using other less obvious properties (hardness, streak, specific gravity, etc). Finally, not all properties of every mineral are equally useful. Generally you will be able to identify a mineral by using only two or three primary properties. These will differ for each mineral. For instance, although pyrite has a hardness of 6 – 6.5, this is not generally a primary property. You will likely be able to identify pyrite by the fact that it is gold colored and has cubic cleavage (3 cleavage planes), thus the color (gold) and cleavage (cubic) will be the primary properties for pyrite. Determine which properties are most valuable in helping you identify each mineral and enter these properties in the last column of your chart. This will be valuable for your study guide. I will distribute an answer key later in the lab, but first try to describe the samples on your own. Figures 3.25 – 3.27 in your lab manual will also help you determine the identity of the minerals (pages 52 – 54). Your manual also contains a mineral database (Figure 3.28, pp. 55 – 59) and additional data sheets for your use (pp. 60 – 65) GREAT RESOURCE ALERT! You can also refer to the website http://web.newsguy.com/dhacat/geo/ for pictures and descriptions of the minerals and rocks. You can find a link to this website on my homepage.
Mineral Identification Chart Sample Number
Color / Streak
Hardness
Number of Cleavage Planes
Shape
Other Properties (luster, transparency)
Mineral Name Primary Properties
Mineral Identification Chart Sample Number
Color / Streak
Hardness
Number of Cleavage Planes
Shape
Other Properties (luster, transparency)
Mineral Name Primary Properties
Mineral Identification Chart Sample Number
Color / Streak
Hardness
Number of Cleavage Planes
Shape
Other Properties (luster, transparency)
Mineral Name Primary Properties
Mineral Identification Chart Sample Number
Color / Streak
Hardness
Number of Cleavage Planes
Shape
Other Properties (luster, transparency)
Mineral Name Primary Properties
Mineral Identification Flow Charts
Color
Cleavage
Hardness Scratches glass
Metallic
Cleavage good to excellent
Distinctive properties gold color, perfect cubic cleavage
Pyrite
High specific gravity, silvery grey
Galena
dark silvery grey to black, 1 plane of Does not scratch glass cleavage, very soft, will leave a black mark when scratched on paper gold color, perfect cubic cleavage
Scratches glass
Cleavage poor or absent
Mineral
Graphite
Pyrite
dark grey to black, will be attracted to a magnet
Magnetite
Brass-yellow color, dark grey streak
Chalcopyrite
dark grey to silver, red Does not scratch glass streak dark grey to black, will be attracted to a magnet
Hematite
Magnetite
Color
Cleavage
Hardness Scratches glass
Distinctive properties
Plagioclase feldpsar
2 planes of cleavage, opaque
Potassium Feldspar
Fizzes w/ HCl when powdered 3 planes of cleavage, fizes readily in HCL
Cleavage good to excellent
Mineral
2 planes of cleavage, striations on surface, slightly translucent
Dolomite Calcite
often colorful (clear, purple, green red, yellow, blue), cubic or octahedral, translucent
Flourite
perfect cubic cleavage and habit, usually transparent, tastes salty
Halite
Does not scratch glass
Light Colored
powdery texture, very soft, basal cleavage may not be apparent clear and transparent, peels into thin sheets opaque, generally, white, grey or green, greasy or soapy texture, can scratch with fingernail
Scratches glass
Does not scratch glass
Muscovite
Talc
clear, white, grey, yellow, can scratch with fingernail
Gypsum
green color conchoidal fracture, rose colored, transparent to translucent opaque, can be namy colors, waxy luster, concoidal fracture
Olivine
transparent to opaque, usually white to grey, conchoidal fracture
Cleavage poor or absent
Kaolinite
powdery texture, very soft, perfect basal cleavage may not be apparent powdery texture, rustybrown to yellow color, dark yellow streak
Rose Quartz Chalcedony
Quartz
Kaolinite
Limonite
Color
Cleavage
Hardness Scratches glass
Distinctive properties
Mineral
2 planes of cleavage, striations on surface
Plagioclase feldpsar
Fizzes w/ HCl when powdered
Dolomite
2 planes of cleavage at Amphibole a 60 to 120 degree angle, black Cleaves into thin sheets
Cleavage good to excellent
Biotite
Does not scratch glass
Dark Colored
often colorful (clear, purple, green red, yellow, blue), cubic or octahedral, translucent
Flourite
2 planes of cleavage at Pyroxene nearly right angles, greenish-black dodecahedral habit (12-sides), deep red
Scratches glass
dark grey to black, will be attracted to a magnet green color opaque, can be namy colors, waxy luster
Garnet Magnetite Olivine Chalcedony
Cleavage poor or absent dark grey to silver, red streak
Hematite
powdery texture, rusty-brown to yellow Does not scratch glass color, dark yellow streak
Limonite
dark grey to black, will be attracted to a magnet
Magnetite
