X'Ray Diffraction and the Identification and Analysis of Clay Minerals SECOND EDITION

DUANE M. MOORE Illinois State Geological Survey

ROBERT C. REYNOLDS, JR. Dartmouth College

Oxford New York OXFORD UNIVERSITY PRESS 1997

Contents

Preface to the Second Edition Preface to the First Edition

xiii xv

1. INTRODUCTION AND HISTORICAL BACKGROUND History The Discovery of X-Rays The Discovery of X-Ray Diffraction History of Clay Mineralogy The Importance of Clay Mineralogy Box 1.1 Clay Minerals as Catalysts The Literature of Clay Mineralogy Summary References

3

2. NATURE AND PRODUCTION OF X-RAYS Box 2.1 Other Methods Safety and Protection Box 2.2 Defining a Dose of Radiation The Nature or X-Rays \ Continuous or White Radiation Characteristic Radiation General Absorption of X-Rays Characteristic Absorption Equipment for Producing and Recording X-Rays Stabilizing the Voltage Generating X-Rays The Diffractometer Step-Scanning with Automated Diffractometers The Single-Crystal Monochromator The Detector Signal Processing Circuitry The Strip-Chart Recorder An Example of a Checklist for Operating XRD Equipment

28 28 31 31 33 33 35 38 40 42 42 43 44 49 52 52 54 55 56

5 6 10 14 17 18 22 23 24

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Contents Summary References

58 59

3. X-RAY DIFFRACTION 61 Scattering 62 Interference ' 64 Scattering from a Row of Atoms 64 Scattering from a Three-Dimensional Array of Atoms 67 Bragg's Law 69 Box 3.1 Diffraction and Reflection 70 The Arithmetic of Scattering 72 The Summation of Scattering Amplitudes 72 The Structure Factor F 77 Information from Intensity 79 The Reciprocal Lattice 80 Real versus Idealized Peaks on XRD Tracings 84 The Interference Function F: Diffraction from a Crystal Whose Unit Cell Has a Unitary Scattering Factor 88 The Lorentz-Polarization Factors 90 Putting It All Together—Building an 001 Diffraction Pattern 92 Exercise: Calculation of the Intensity from d(001) for Illite 97 Points to Remember 103 References 103

4. STRUCTURE AND PROPERTIES: GENERAL TREATMENT

104

General Structural Features Tetrahedral Sheets Octahedral Sheets Dioctahedral and Trioctahedral Joining the Sheets Stacking the Layers Properties ' Total Charge, Layer or Permanent Charge, and Variable Charge Electric Double Layer Exchangeable Ions or Cation-Exchange Capacity Interaction of Water with Clay Mineral Surfaces Interaction with Organic Compounds Classification Box 4.1 Nomenclature References 5. STRUCTURE, NOMENCLATURE, AND OCCURRENCES OF CLAY MINERALS The Individual Clay Minerals The 1:1 Layer Type

104 104 105 106 107 112 117 118 120 121 123 126 130 132 134 138 13 8 138

Contents Serpentine minerals Berthierine Odinite Kaolin minerals Box 5.1 Uses of Kaolinite Allophane and imogolite The 2:1 Layer Type, x = 0 The 2:1 Layer Type, x ~ 1 The trioctahedral subgroup The dioctahedral subgroup . The 2:1 Layer Types with x < 1 Illite Glauconite Smectite Box 5.2 Alteration of Ash-Fall Layers Vermiculite Chlorite Mixed-Layered Clay Minerals Mixed-layering, interlayering, and interstratification Illite/smectite (I/S) Box 5.3 Reichweite or Ordering Models for smectite-to-illite transition MacEwan crystallite model Fundamental particle model Two-solid-solution model Chlorite/smectite (C/S) Serpentine/chlorite Kaolinite/expandables (K/E) Sepiolite and Palygorskite The Origin of Clay Minerals Summary Exercise: Calculating Structural Formulas Exercise: Making Structural Models of Layer Silicates References 6. SAMPLE PREPARATION TECHNIQUES FOR CLAY MINERALS Evaluating the Sample Disaggregating the Rock Separating Clay Minerals from Clastic Rocks Separating Clay Minerals from Carbonate Rocks Separating Clay Minerals from Sulfate Rocks Separating Clay Minerals from Unconsolidated Materials Box 6.1 Glacial Deposits, North American Interior

139 139 139 140 144 145 146 146 147 147 148 149 153 155 158 158 162 167 168 170 171 176 177 177 179 181 183 184 185 186 188 189 192 195

204 204 206 206 207 207 208 208

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Contents Chemical Pretreatments Removal of Iron Oxides Removal of Organic Materials Saturating the Clay Minerals with Different Cations Particle-Size Separation Preparing the Oriented Clay Mineral Aggregates The Glass Slide Method The Smear Mount Method The Millipore® Filter Transfer Method The Centrifuged Porous Plate Method Dealing with Curlers or Peelers Making the Random Powder Mount Everyday random powder packs Freeze-dried random powder packs Ethylene Glycol Solvation Final Note References

209 209 209 210 211 214 214 215 216 218 219 220 222 222 224 225 225

7. IDENTIFICATION OF CLAY MINERALS AND ASSOCIATED MINERALS Clay Mineral Identification—General Principles Illite and Glauconite Chlorite and Kaolinite Vermiculite Smectite Sepiolite, Palygorskite, and Halloysite 060 Reflections The Use of hkl Reflections for the Determination of Polytypes Chlorite Polytypes , The Kaolin Polytypes The Micas, Illite, and Glauconite Nonclay Minerals Silica Minerals Feldspar Zeolites Carbonates Apatite, Pyrite, and Jarosite Gypsum, Anhydrite, Celestite, and Barite Lepidocrocite, Goethite, Gibbsite, and Anatase Summary References

227 228 233 233 239 241 243 244 246 246 247 247 248 250 252 254 255 256 257 258 259

8. IDENTIFICATION OF MIXED-LAYERED CLAY MINERALS M6ring' s Principles and Mixed-Layered Nomenclature The Q Rule, a Broadening Descriptor

261 263 266

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Contents Mixed-Layered Clay Minerals Illite/Smectite Chlorite/Smectite and Chlorite/Vermiculite Kaolinite/Smectite Serpentine/Chlorite Mica/Vermiculite Summary References 9. QUANTITATIVE ANALYSIS Required Sample Characteristics Sample Length Sample Thickness Sample Position Homogeneity of the Sample Equations for Quantitative Analysis Basic Quantitative Diffraction Equation Derivation of a Working Form of the Equation for Analysis The Method of the Orienting Internal Standard Mineral Reference Intensities General Comments Calculated Mineral Reference Intensities Practical Examples of the Application of Reference Intensities Measurement of Peak Intensity Comments and Summary References

270 270 276

10. DISORDER IN SMECTITE, ILLITE/SMECTITE, AND ILLITE Small Crystals in Reciprocal Space Turbostratic Disorder v Theory Smectite Illite/Smectite Rotational Disorder in Illite and Illite/Smectite Cis-Vacant Elite and Interstratified Cis- and Trans-Vacant Illite/Smectite Conclusions References

330 331 335 335 339 339 341

APPENDIX: MODELING ONE-DIMENSIONAL X-RAY PATTERNS The Input Variables Simulating the Instrument Describing the Clay Mineral Theory Structures of the Component Layers Advanced Techniques Pure Minerals

284 289 292 296 296 298 299 300 301 306 307 308 308 313 316 317 317 318 321

321 327 329

349 356

357 359 360

360

360 362 366 368 369

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Contents Compositional Superstructures Layer Types Not Specifically Included Atom Types Not Incorporated in the Model Defect Broadening References ,

INDEX

369 369 370 370 371 373