Minerals of the Montmorillonite Group Their Origin and Relation to Soils and Clays
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If yon no longer need this publication write to the Geological Survey in Washington for an official mailing label to use in returning it UNITED STATES DEPARTMENT OF THE INTERIOR MINERALS OF THE MONTMORILLONITE GROUP THEIR ORIGIN AND RELATION TO SOILS AND CLAYS GEOLOGICAL SURVEY PROFESSIONAL PAPER 205-B UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director Professional Paper 205-B MINERALS OF THE MONTMORILLONITE GROUP THEIR ORIGIN AND RELATION TO SOILS AND CLAYS BY CLARENCE S. ROSS AND STERLING B. HENDRICKS Shorter contributions to general geology, 1943-44 (Pages 23-79) UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1945 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 55 cents CONTENTS Page Page Abstract............. ........................... 23 Mineralogy of the montmorillonite group—Continued. Introduction.......... ............................ 23 Derivation of formulas—Continued. Methods of study. ........................... 24 Saponite-hectorite series...................... 46 Previous work.... ........................... 24 Suggested formulas........................... 47 Acknowledgments. ........................... 25 Thermal studies...................................... 48 Nomenclature........ ........................... 25 Essential hydroxyl............................... 48 Montmorillonite.. ........................... 25 Interlayer water................................. 52 Beidellite........ ........................... 26 Optical properties.................................... 54 Saponite........................................ 26 Methods of determination......................... 54 Hectorite....................................... 27 Determinations of indices of refraction.............. 55 Nontronite...................................... 27 Pleochroism..................................... 57 Volchonskoite................................... 28 Electron-microscope photographs....................... 57 Kaolin minerals.................................. 28 Synthesis........................................... 58 Hydrous micas (illite)............................ 28 Origin and mode of occurrence................ ..... 60 Mixed-layer minerals................................. 29 General features........................ ..... 60 Crystal structure..................................... 29 Soils and rock weathering................ ..... 61 Location and description of analyzed-clays.............. 30 Discussion......................... ..... 61 Montmorillonite-beidellite series................... 30 Australian soils..................... ..... 62 Nontronites..................................... 32 Piedmont soils...................... ..... 62 Samples from soils and chromium-bearing samples... 32 Java soils.......................... ..... 63 Saponite-hectorite series .......................... 32 Glacial soils........................ ..... 63 Samples containing silica or an iron-bearing impurity 32 Summary of soils and rock weathering. ..... 64 Chemical analyses.................................... 34 Bentonites............................. ..... 64 Impurities in clays................................... 36 Structure of parent glass............. ..... 64 Minor constituents................................... 37 Physical properties........................... 65 Base exchange....................................... 37 Definition........................... ..... : . 65 Physical chemistry of base exchange................ 37 Mode of occurrence.......................... 65 Determinations of exchangeable bases.............. 38 Ordovician bentonite......................... 67 Mineralogy of the montmorillonite group................ 39 Volcanic materials at Magnet Cove, Ark............ 67 General relations................................. 39 Methods of calculation of mineral formulas.......... 41 Clays of the geyser region in Yellowstone Park...... 68 Derivation of formulas............................ 44 Vein and gouge clays............................. 69 Montmorillonite-beidellite series............... 44 Pyrophyllite and talc................................. 70 Nontronite.................................. 45 Bibliography........................................ 72 Montmorillonite-beidellite-nontronite series...... 46 Index............................................... 79 Ill IV CONTENTS ILLUSTRATIONS Page PLATE 1. Alteration of volcanic materials to montmorillonite and kaolinite............................................ 58 2. A, B, and C, Alteration of volcanic materials to montmorillonite and kaolinite; D, Varved sedimentary clay...... 58 3. A, Bentonite showing volcanic-ash structure; B, Vein clay with clay-filled joint cracks; C, Granite gneiss with plagi-v clase altered to beidellite; D, Plagioclase phenocryst in rhyolite partly altered to montmorillonite.............. 58 4. Bentonite showing volcanic-ash structure................................................................. 58 5. Alteration of various rock types to montmorillonite and associated minerals.................................. 58 6. Magnesium and iron-rich clays.......................................................................... 58 7. A, Beidellite replacement of molluscan shell; B, Montmorillonite from pegmatite; C and D, Electron micrograpl "" of clays............................................................................................ 58 8. Electron micrographs of hectorite and nontronite.......................................................... 58 FIGURE 5, 6, and 7. Dehydration curves of montmorillonite clays..................................................... 49-51 8. Curves showing relation of vapor pressure to cleavage spacing in montmorillonite............................. 53 9. Curves showing relation of indices of refraction to ferric iron in minerals of the montmorillonite-nontronite'series 56 TABLES Page TABLE 1. Analyses of montmorillonite-beidellite series.............................................................. 34 2. Analyses of nontronite................................................................................. 35 3. Analyses of samples from soils and chromium-bearing specimens from Russia................................. 35 4. Analyses of hectorite and saponite....................................................................... 35 5. Analyses of samples containing excess silica............................................................... 35 6. Analyses of nontronites containing an iron-bearing impurity................................................ 35 7. Analyses of specimens containing chlorite, vermiculite, or other iron-bearing impurity.......................... 35 8. Analyses of hectorite and a clay from Amargosa Valley before and after treatment with ammonium acetate...... 38 9. Base-exchange capacities of some montmorillonite clays.................................................... 39 10. Relation of ions to crystal structure..................................................................... 42 11. Calculations of impurities in representative clays.......................................................... 43 12. Proportions of end members in selected samples........................................................... 46 13. Indices of refraction and birefringence as affected by the presence of ferric iron in the montmorillonite-nontroni^e series.............................................................................................. 55 14. Indices of refraction of clays determined on films.......................................................... 57 15. Indices of refraction determined on clay grains............................................................ 57 16. Indices of refraction of minerals related to the montmorillonite group........................................ 57 17. Indices of refraction of clays dehydrated at 210° C......................................................... 57 18. Conditions of synthesis for hydrous aluminum silicates..................................................... 59 19. Analyses of bentonite and related rocks, Santa Monica Mountains, Calif...................................... 66 20. Analyses of pyrophyllite and talc...................................................................... 70 MINERALS OF THE MONTMORILLONITE GROUP THEIR ORIGIN AND RELATION TO SOILS AND CLAYS By CLARENCE S. Ross, Geological Survey, United States Department of the Interior, and STERLING B. HEN- DRICKS, Bureau of Plant Industry, Soils, and Agricultural Engineering, United States Department of Agriculture. ABSTRACT A detailed study has been made of the montmorillonite group but potassium, magnesium, hydrogen, and aluminum may be of clay minerals, one of the most widely occurring of all mineral exchangeable. materials. Minerals of this group are exceedingly fine grained crystalline aggregates, and they present an unusually wide range The composition and mineral relations of the clay minerals are in composition. Essential information on the group was obtained intimately related to the conditions under which they form. In only after study, by all available mineralogical methods, of more general, alkalic feldspars and the micas tend to alter to kaolin than 100 carefully selected specimens. This information has minerals, whereas ferromagnesian minerals, calcic feldspar?, and made possible the determination of the limits of variation in com volcanic glasses commonly alter to members