Hydrous phyllosilicates (exclusive of micas) / S.W.Bailey et al.; ed. by S.W.Bailey. - Washington: Mineralogical Society of America, 1988 (1991). - xiii, 725 p.: ill. - (Reviews in mineralogy; vol.19). - Bibliogr. at the end of the chapters. - ISBN 0-939950-23-5; ISSN 0275-0279  Место хранения:   018 | Институт нефтегазовой геологии и геофизики им. А.А.Трофимука | Новосибирск | Библиотека

Оглавление / Contents

Copyright; Additional Copies ................................... ii Foreword; Dedication .......................................... iii Preface and Acknowledgments ................................... xii Chapter 1 S.W. Bailey Introduction Structural definitions ....................................... 1 LATERAL FIT OF SHEETS WITHIN A LAYER ............................ 3 Tetrahedral rotation ......................................... 4 Other structural adjustments ................................. 5 UNIT CELLS ...................................................... 5 CLASSIFICATION .................................................. 6 REFERENCES ...................................................... 8 Chapter 2 Polytypism of 1:1 Layer Silicates S.W. Bailey INTRODUCTION .................................................... 9 DERIVATION OF STANDARD POLYTYPES ............................... 11 Assumptions ................................................. 11 Derivation of 12 standard polytypes ......................... 12 IDENTIFICATION OF NATURAL SPECIMENS ............................ 16 Trioctahedral species ....................................... 16 X-ray powder patterns .................................... 16 Single crystal patterns .................................. 17 Trioctahedral 1:1 polytypes found in nature .............. 22 Dioctahedral species ........................................ 22 RELATIVE STRUCTURAL STABILITIES ................................ 23 ACKNOWLEDGMENTS ................................................ 26 REFERENCES ..................................................... 26 Chapter 3 Kaolin Minerals: Structures and Stabilities R.F. Giese, Jr. INTRODUCTION ................................................... 29 KAOLIN-GROUP MINERALS .......................................... 29 Crystallography ............................................. 30 Structure refinements ....................................... 32 Refined structures ....................................... 34 Hydroxy I hydrogen positions ............................. 38 Defect structure ............................................ 43 Spectroscopic studies ....................................... 48 Infrared spectroscopy .................................... 48 Electron paramagnetic resonance spectroscopy ............. 50 Nuclear magnetic resonance ............................... 52 HALLOYSITES .................................................... 53 Structure ................................................... 56 Interlayer water ............................................ 57 Identification .............................................. 60 SUMMARY ........................................................ 60 ACKNOWLEDGMENTS ................................................ 61 REFERENCES ..................................................... 62 Chapter 4 Kaolin minerals: their Genesis and 0ccurents H.H. Murray INTRODUCTION ................................................... 67 GENESIS ........................................................ 69 OCCURRENCES OF SELECTED KAOLIN DEPOSITS ........................ 72 HYDROTHERMAL KAOLIN DEPOSITS ................................... 73 China; Italy; Japan ......................................... 73 Mexico; United States ....................................... 74 RESIDUAL KAOLIN DEPOSITS ....................................... 75 Argentina; Australia ........................................ 75 China; Czechoslovakia; German Democratic Republic; Indonesia ................................................... 76 USSR; South Africa .......................................... 78 MIXED HYDROTHERMAL AND RESIDUAL KAOLIN DEPOSITS ................ 78 Cornwall, England ........................................... 78 New Zealand ................................................. 80 SEDIMENTARY KAOLIN DEPOSITS .................................... 80 Australia; Brazil ........................................... 80 Federal Republic of Germany ................................. 82 Spain; Suriname ............................................. 83 United States ............................................... 84 SUMMARY ........................................................ 86 REFERENCES ..................................................... 87 Chapter 5 SERPENTINE MINERALS: STRUCTURES AND PETROLOGY F.J. Wicks & D.S. O'Hanley INTRODUCTION ................................................... 91 CRYSTAL STRUCTURES ............................................. 91 Lizardite ................................................... 92 Structural refinements ................................... 93 Electron microscopy ...................................... 98 Composition .............................................. 99 Chrysotile ................................................. 101 Cylindrical poly types .................................. 104 Structural refinements .................................. 106 Electron microscopy ..................................... 109 Polygonal serpentine .................................... 111 Composition ................................................ 113 Antigorite ................................................. 114 Structural refinements .................................. 115 Electron microscopy ..................................... 119 Composition ............................................. 122 Carlosturanite ............................................. 123 IDENTIFICATION ................................................ 124 X-ray powder diffraction ................................... 125 Lizardite ............................................... 125 Chrystotile; Antigorite ................................. 128 Single-crystal diffraction ................................. 128 Lizardite; Antigorite ................................... 129 Fiber diffraction .......................................... 129 Chrysotile .............................................. 129 Antigorite .............................................. 130 Microbeam camera ........................................... 131 HRTEM studies .............................................. 131 TEXTURES IN SERPENTINITES ..................................... 132 СASSIAR ASBESTOS MINE ......................................... 135 Serpentine textures and their distribution ................. 137 TRANSITIONS AMONG SERPENTINE MINERALS AND TEXTURES ............ 140 STABLE ISOTOPES ............................................... 142 SERPENTINE PHASE DIAGRAM ...................................... 145 MgO-SiO2-H20 system ........................................ 146 Serpentine-out reactions ................................... 148 MgO-Al2O3-SiO2-H2O system .................................. 148 FeO-Fe2O3-MgO-Al2O3-SiO2-H20 system ........................ 149 Other components ........................................... 150 Discussion of phase diagram ................................ 153 Importance of water pressure ............................... 151 Types of serpentinization .................................. 155 THE ROLE OF FRACTURES AND DEFORMATION ......................... 156 CHRYSOTILE ASBESTOS DEPOSITS .................................. 157 ACKNOWLEDGMENTS ............................................... 159 REFERENCES .................................................... 159 Chapter 6 Structures and compositions of Other Trioctahedral 1:1 Phyllosilicates S.W. Bailey AMESITE ....................................................... 169 BERTHIERINE ................................................... 179 ODINITE ....................................................... 181 CRONSTEDTITE .................................................. 182 NI-RICH SPECIES ............................................... 184 Nepouite ................................................... 184 Pecoraite .................................................. 185 ACKNOWLEDGMENTS ............................................... 186 REFERENCES .................................................... 186 Chapter 7 Isotopic Studies of phyllosilicates S.M. Savin & M. Lee INTRODUCTION .................................................. 189 Isotopic fractionations .................................... 189 Terminology and notation ................................... 189 Factors controlling isotopic compositions of minerals ...... 190 Isotopic compositions of natural waters ................. 191 Temperature dependence of isotopic fractionations ....... 191 KINETICS OF MINERAL-WATER ISOTOPIC EXCHANGE ................... 192 Exchange rates inferred from δD and δ18O values in natural systems ............................................ 193 Exchange rates inferred from laboratory experiments ........ 194 Discussion of mineral-water exchange kinetics .............. 196 EQUILIBRIUM ISOTOPE FRACTIONATIONS ............................ 196 The approaches ............................................. 196 Laboratory equilibration experiments .................... 196 Naturally occurring samples ............................. 197 Statistical mechanical calculations ..................... 197 Empirical bond-type calculations ........................ 199 Estimates of mineral-water fractionations .................. 203 Kaolinite ............................................... 203 Pyrophyllite ............................................ 204 Gibbsite; Smectite, mixed-layer illitelsmectite, and illite .................................................. 207 Serpentine .............................................. 211 Chlorite ................................................ 213 Talc; Brucite ........................................... 216 CONCLUSIONS ................................................... 218 ACKNOWLEDGMENTS ............................................... 218 REFERENCES .................................................... 219 Chapter 8 Talc, Pyrophyllite, and Related Minerals B.W. Evans & S. Guggenheim INTRODUCTION .................................................. 225 General .................................................... 225 Talc and pyrophyllite ...................................... 225 NOMENCLATURE AND GENERAL CHEMICAL CLASSIFICATION .............. 226 Pyrophyllite; Talc ......................................... 226 CRYSTAL STRUCTURE STUDIES ..................................... 229 Pyrophyllite ............................................... 232 Pyrophyllite dehydroxylate ................................. 240 Talc ....................................................... 241 SPECTROSCOPIC STUDIES ......................................... 242 Infrared spectra ........................................... 242 Talc .................................................... 244 Pyrophyllite ............................................ 246 Mossbauer spectra .......................................... 246 Talc .................................................... 246 Pyrophyllite ............................................ 247 Nuclear magnetic resonance ................................. 248 Other spectroscopic studies ................................ 249 THERMAL DECOMPOSITION ......................................... 250 Pyrophyllite ............................................... 251 Talc ....................................................... 255 PETROLOGY AND PHASE EQUILIBRIA ................................ 257 Parageneses of pyrophyllite ................................ 259 Parageneses of talc ........................................ 265 Talc in ultramafic rocks ................................ 265 Talc in siliceous dolomites ............................. 269 Hydrothermal and other low-temperature parageneses of talc .................................................... 272 Talc in high-pressure rocks ............................. 275 Parageneses of minnesotaite ................................ 276 ACKNOWLEDGMENTS ............................................... 280 REFERENCES .................................................... 280 Chapter 9 Stability, Phase relations, and thermodynamic properties of chlorite and serpentine group minerals J.V. Chernosky, Jr., R.G. Berman & L.T. Bryndzia INTRODUCTION .................................................. 295 EVALUATION OF PHASE EQUILIBRIUM DATA AND THERMODYNAMIC ANALYSIS ...................................................... 300 PHASE RELATIONS OF SERPENTINE GROUP MINERALS .................. 301 Antigorite .................................................... 301 Chrysotile ................................................. 302 Lizardite .................................................. 305 Petrogenetic grids involving serpentine minerals ........... 306 Garnierite and greenalite .................................. 311 STABILITY OF ALUMINOUS LIZARDITE .............................. 314 Synthesis of Lz(ss) with x > 0.8 ........................... 314 Stability of lizardite (x > 0.8) ........................... 314 STABILITY OF Fe, MG-CHLORITE .................................. 316 Phase relations of Mg-chlorite with РH2О) = P(Total) ....... 318 Stability of Mg-chlorite in H2O-CO2 fluids ................. 321 STABILITY OF Fe, MG-CHLORITE .................................. 321 The stability of Fe-chlorite ............................... 326 The stability of intermediate Fe, Mg-chlorite .............. 330 Thermodynamic analysis ..................................... 336 Geological application of chlorite redox equilibria ........ 337 SUGGESTIONS FOR FUTURE WORK ................................... 341 ACKNOWLEDGMENTS ............................................... 341 REFERENCES .................................................... 341 Chapter 10 Chlorites: Structures and Crystal Chemistry S.W. Bailey INTRODUCTION .................................................. 347 NOMENCLATURE .................................................. 348 CHEMICAL COMPOSITION .......................................... 349 STRUCTURAL TYPES .............................................. 353 Layer-interlayer units ..................................... 353 Regular-stacking polytypes ................................. 357 Semi-random stacking ....................................... 362 IDENTIFICATION ................................................ 362 X-ray study ................................................ 362 Oriented aggregates ..................................... 362 Random power mounts ..................................... 364 Single crystals ......................................... 366 Optical properties ......................................... 372 Infrared absorption ........................................ 376 Mossbauer analysis ......................................... 378 DETERMINATION OF COMPOSITION .................................. 378 Direct analysis ............................................ 378 Indirect analysis .......................................... 379 CRYSTAL CHEMISTRY ............................................. 381 Structural stabilities ..................................... 381 Environmental significance of polytypes .................... 384 Variation of composition with temperature and genesis ...... 385 Structural details of trioctahedral IIb chlorite ........... 385 Triclinic symmetry ...................................... 385 Monoclinic symmetry ..................................... 390 General observations .................................... 391 Structural details of trioctahedral la chlorite ............ 391 Structural details of the trioctahedral lb chlorite ........ 392 Orthorhombic-shaped cell ................................ 392 Monoclinic-shaped cell .................................. 392 Multi-layer trioctahedral chlorites ........................ 392 Di, trioctahedral chlorite ................................. 393 Cookeite ................................................ 393 Sudoite ................................................. 395 Dioctahedral donbassite .................................... 395 Octahedral compositions outside the Mg-Fe-Al system ........ 396 Pennantite ................................................. 396 Nimite ..................................................... 396 Bailey' More ............................................... 397 Related structures ......................................... 397 Franklinfurnaceite ...................................... 397 Gonyerite ............................................... 398 ACKNOWLEDGMENTS ............................................... 398 REFERENCES .................................................... 398 Chapter 11 Chlorites: Metamorphic Petrology J. Laird INTRODUCTION .................................................. 405 Petrography ................................................ 405 Interpretation of chlorite compositions .................... 406 BULK ROCK COMPOSITION ......................................... 406 PELITIC ROCKS ................................................. 411 Mineralogical questions .................................... 411 Returning to the rocks ..................................... 413 Diagenesis to chlorite grade ............................... 413 Biotite isograd ............................................ 414 Garnet isograd ............................................. 415 More Tschermak substitution ................................ 415 Petrogenetic grid .......................................... 415 Medium-pressure facies series ........................... 416 Low-pressure facies series metamorphism ................. 418 FeMg-1 substitution ........................................ 419 Fluid phase ................................................ 420 High-pressure facies series ................................ 420 FELSIC ROCKS .................................................. 422 Diagenesis to zeolite facies ............................... 422 Prehnite-pumpellyite to greenschist facies ................. 422 Felsic volcanic rocks ...................................... 425 МАFIC ROCKS ................................................... 425 Diagenesis to greenschist facies ........................... 427 Greenschist to amphibolite facies .......................... 429 Fe-rich mafic compositions ................................. 430 Contact metamorphism ....................................... 430 Blueschist and eclogite .................................... 433 Garbenschiefer ............................................. 433 ALUMINOUS CALC-SILICATE ROCK .................................. 433 Medium-pressure facies series .............................. 435 Low-pressure facies series regional metamorphism ........... 435 Contact metamorphism ....................................... 436 Metasomatism, including rodingite .......................... 436 ULTRAMAFIC ROCKS .............................................. 437 Contact metamorphism ....................................... 437 Metasomatism ............................................... 437 IRON FORMATIONS ............................................... 437 MN-RICH ROCKS ................................................. 440 GEOTHERMOMETRY AND GEOBAROMETRY ............................... 440 Amphibole-chlorite ......................................... 440 Garnet-chlorite ............................................ 442 Chloritoid-chlorite ........................................ 443 Biotite-chlorite ........................................... 443 CONCLUDING REMARKS ............................................ 443 ACKNOWLEDGMENTS ............................................... 445 APPENDIX ...................................................... 445 REFERENCES .................................................... 447 Chapter 12 VERMICULITE C. de la Calle & H. Suquet INTRODUCTION .................................................. 455 GEOLOGY OF VERMICULITE ........................................ 455 Parentage .................................................. 455 Occurrences of macroscopic vermiculites .................... 456 Characteristics of some vermiculite deposits ............... 457 Santa Olalla, Spain; Benahavis, Spain; Malawi, Nyasaland ............................................... 457 Kenya; Prayssac, France ................................. 458 OPTICAL PROPERTIES ............................................ 458 CHEMICAL COMPOSITION AND CRYSTAL CHEMISTRY .................... 458 Chemical analyses .......................................... 459 Structural formula ......................................... 459 Distribution of Si-Al substitutions ........................ 460 Thermal properties ......................................... 461 SAMPLES FOR CRYSTAL STRUCTURE STUDIES ......................... 461 CRYSTAL STRUCTURE ............................................. 463 X-ray diffraction studies .................................. 463 Appearance of the levels h0l, 0kl, and 1kl for a semi- ordered structure .......................................... 464 Quantitative analysis of diagrams of semi-ordered structures ................................................. 464 Appearance of the hOl reflections corresponding to the ordered ............................................. 464 projection ................................................. 464 Analysis of the 0kl and 1kl levels ......................... 466 Research on the position of the maxima ..................... 466 Calculation of the diffracted intensity I(l) ............... 468 Analysis of abnormal diffraction of X-rays ................. 469 Description of stacking of layers in ordered vermiculite structures ..................................... 471 Ca vermiculite (d(001) = 14.92 Å). V3 stacking type ........ 471 Na vermiculite (d(001) = 14.83 Å). V3 stacking type ........ 473 Anhydrous K, Rb, Cs, and Ba vermiculites (d(001) = 10 Å) ...................................................... 473 Vermiculites with LiH2O (d(001) = 10.1 Å) .................. 475 Vermiculite-aniline complex ................................ 475 Description of stacking layers in semi-ordered vermiculite structures ..................................... 475 Hydrated vermiculite phases studied quantitatively along the three axes X, Y, Z ............................... 476 Mg vermiculite (d(001) = 14.3 Å). V1 stacking type ......... 476 Na vermiculite (d(001) = 11.85 Å). Vc stacking type ........ 477 Hydrated vermiculites studied quantitatively in two dimensions ................................................. 480 Ba•6H20 vermiculite (d(001) = 12.2 Å). Vd stacking type ....................................................... 480 Sr•3.3 H2O vermiculite (d(001) = 11.85 Å). Va stacking type ....................................................... 480 Hydrated and anhydrous vermiculite phases studied in the direction perpendicular to the layers, using one-dimensional Fourier projections ........................ 482 Ы-2.4Н20 vermiculite (d(001) = 12.2 Å). Vb stacking type ....................................................... 482 Sr-4H20 vermiculite (d(001) = 12.08 Å). Ve stacking type ....................................................... 482 Са-4Н2О vermiculite (d(001) = 11.74 Å) Ve stacking type ....................................................... 482 Sr vermiculite (d(001) = 9.78 Å). Ca vermiculite (d(001) = 9.50. A) ......................................... 482 Na vermiculite (d(001) = 9.6 Å). Li vermiculite (d(001) = 9.4 A) .................................................. 482 Hydrated vermiculites studied qualitatively ................ 482 Ca vermiculite (d(001) = 14.70 Å). V5 stacking type ........ 482 Mg vermiculite (d(001) = 13.8 Å). V7 stacking type ......... 483 Vermiculite-organic interlayer complexes ................... 483 Range of stability for various crystalline phases of vermiculite ................................................ 484 Cation exchange and layer shifts ........................... 484 Factors that determine the crystal structure of a vermiculite ................................................ 486 Role of the interlayer material ............................ 486 Role of "inherited" factors; Role of texture ............... 487 Jelly-like structure of vermiculite: Macroscopic swelling ................................................... 488 Structures belonging to vermiculites with 2M1 parentage .................................................. 489 COMPARISON OF PROPERTIES OF VERMICULITES AND HIGH CHARGE SMECTITES ..................................................... 489 ACKNOWLEDGMENTS ............................................... 492 REFERENCES .................................................... 492 Chapter 13 Smectites N. Guven INTRODUCTION .................................................. 497 BASIC STRUCTURAL ELEMENTS OF SMECTITES ........................ 498 Octahedral sheets .......................................... 498 Tetrahedral sheets ......................................... 503 Interlayer configurations .................................. 506 Stacking of layers ......................................... 507 Classification ............................................. 509 DIOCTAHEDRAL SMECTITES ........................................ 510 Structural and morphological variations .................... 511 Montmorillonite ......................................... 511 Beidellite .............................................. 517 Nontronite .............................................. 517 Volkonskoite ............................................ 521 Vanadium smectite ....................................... 523 Chemical variations ........................................ 526 Statistical analysis of the chemical data ............... 526 TRIOCTAHEDRAL SMECTITES ....................................... 530 Smectite synthesis at low temperatures ..................... 531 Trioctahedral magnesian smectites with Li+ substitutions or vacancies in octahedra .................... 535 Hectorite ............................................... 435 Stevensite .............................................. 539 Swinefordite ............................................ 540 Trioctahedral smectites of the transition metals ........... 542 Sauconite ............................................... 542 Nickel smectite; Cobalt smectite ........................ 544 Manganese smectite ...................................... 545 Trioctahedral ferromagnesian smectites ..................... 546 Saponite ................................................ 547 Iron Saponite ........................................... 549 ACKNOWLEDGMENTS ............................................... 552 REFERENCES .................................................... 552 Chapter 14 VECTOR REPRESENTATION OF PHYLLOSILICATE COMPOSITIONS D.M. Burt INTRODUCTION .................................................. 561 VECTOR REPRESENTATIONS ........................................ 562 SIMPLE PHYLLOSILICATES ........................................ 565 1:1 PHYLLOSILICATES AND ISOCHEMICAL 2:1 CHLORITES ............. 568 TALC AND PYROPHYLLITE: 2:1 PHYLLOSILICATES .................... 571 OCTAHEDRAL LITHIUM ............................................ 574 INTERLAYER CHARGE (POTASSIUM AND SODIUM) ...................... 577 DIVALENT INTERLAYER CATIONS (CALCIUM AND BARIUM) .............. 580 OCTAHEDRAL TITANIUM ........................................... 585 FERROUS AND FERRIC IRON, PLUS HYDROGEN ........................ 589 SUMMARY AND CONCLUSIONS ....................................... 594 ACKNOWLEDGMENTS ............................................... 596 REFERENCES .................................................... 596 Chapter 15 Mixed Layer Chlorite Minerals R.C. Reynolds, Jr. INTRODUCTION .................................................. 601 MDCED-LAYER CLAY MINERALS ..................................... 601 Statistical description of ordering ........................ 601 Names of mixed-layered chlorite minerals ................... 602 Identification of random and ordered interstratification ........................................ 602 MDCED-LAYER CHLORITE MINERALS ................................. 606 THE STRUCTURES OF MDCED-LAYERED CHLORITE MINERALS ............. 606 Assignment of atoms to the unit cell ....................... 606 IDENTIFICATION AND CHARACTERIZATION OF MIXED-LAYERED CHLORITES ..................................................... 608 Sample preparation ......................................... 608 001 X-RAY DIFFRACTION PATTERNS FOR MDCED-LAYERED CHLORITES ..................................................... 611 Ordered (R1) structures .................................... 611 Random (R = 0) structures .................................. 613 GEOLOGICAL OCCURRENCES OF NON-EXPANDABLE MDCED-LAYERED CHLORITE MINERALS ............................................. 620 GEOLOGICAL OCCURRENCES OF EXPANDABLE MDCED-LAYERED CHLORITE MINERALS ............................................. 622 APPENDDC ...................................................... 625 REFERENCES .................................................... 626 Chapter 16 Sepiolite and Palygorskite B.F. Jones & E. Galan INTRODUCTION .................................................. 631 STRUCTURES .................................................... 632 CHEMISTRY ..................................................... 639 PHYSICAL, PHYSICO-CHEMICAL AND THERMAL PROPERTIES ............. 641 Physical properties ........................................ 641 Sorptive properties ........................................ 644 Surface area modifications ................................. 645 Rheological properties ..................................... 646 Thermal behavior ........................................... 648 OCCURRENCES AND ORIGINS ....................................... 651 Locations and time distribution ............................ 651 Synthesis and stability .................................... 653 Environments ............................................... 655 Marine .................................................. 655 Continental - soils, calcretes and alluvium ............. 656 Continental - lacustrine ................................ 661 Association with igneous rocks ............................. 661 Summary .................................................... 661 APPLICATIONS .................................................. 663 Sorptive applications ...................................... 663 Organo-mineral derivatives ................................. 666 Catalytic application ...................................... 666 Rheological applications ................................... 666 New applications ........................................... 667 ACKNOWLEDGMENTS ............................................... 667 REFERENCES .................................................... 667 Chapter 17 Crystal Chemistry, Classification, and Identification of Modulated Layer Silicates S. Guggenheim & R.A. Eggleton INTRODUCTION .................................................. 675 GEOMETRIC CONCEPTS ............................................ 675 Structures with continuous octahedral sheets ............... 676 Reducing relatively large tetrahedral sheets ............ 676 Enlarging relatively small tetrahedral sheets ........... 678 Avoiding sheet-like tetrahedral linkages ................ 680 Structures with discontinuous octahedral sheets ............ 682 COMPOSITIONAL FACTORS ......................................... 684 ENVIORNMENTAL FACTORS ......................................... 686 POLYSOMATIC AND HOMOLOGOUS SERIES ............................. 687 MODULATED 1: L LAYER SILICATE STRUCTURES ...................... 688 Antigorite ................................................. 688 Carlosturanite ............................................. 691 Baumite; Greenalite ........................................ 692 Caryopilite; Pyrosmalite group ............................. 694 Bementite .................................................. 696 MODULATED 2:1 LAYER SILICATE STRUCTURES ....................... 698 Island structures .......................................... 698 Zussmanite .............................................. 698 Stilpnomelane ........................................... 700 Parsettensite ........................................... 701 Bannisterite ............................................ 702 Strip structures ........................................... 702 Minnesotaite ............................................ 702 Ganophyllite ............................................ 706 Gonyerite ............................................... 707 IDENTIFICATION ................................................ 707 CLASSIFICATION ................................................ 710 General .................................................... 710 Discussion ................................................. 713 ACKNOWLEDGMENTS ............................................... 714 REFERENCES .................................................... 714 APPENDIX: POWDER X-RAY DIFFRACTION DATA FOR MODULATED LAYER SILICATES ............................................... 719