Hostname: page-component-cd9895bd7-gxg78 Total loading time: 0 Render date: 2024-12-28T22:34:50.515Z Has data issue: false hasContentIssue false
  • English
  • Français

Transmission Electron Microscopic Study of Coexisting Pyrophyllite and Muscovite: Direct Evidence for the Metastability of Illite

Published online by Cambridge University Press:  02 April 2024

Wei-Teh Jiang ,
Eric J. Essene  and
Donald R. Peacor
Wei-Teh Jiang
Affiliation:
Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109
Eric J. Essene
Affiliation:
Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109
Donald R. Peacor
Affiliation:
Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Transmission electron microscopy has been used to characterize coexisting pyrophyllite and muscovite in low-grade metamorphosed pelites from Witwatersrand and northeastern Pennsylvania. The Witwatersrand sample consisted largely of porphyroblasts of interlayered muscovite and pyrophyllite in a fine-grained matrix of the same phases. In both textures, muscovite and pyrophyllite occurred as interlayered packets (with apparently coherent interfaces) from about 300 Å to a few micrometers in thickness, with no mixed layering. Their compositions were determined with a scanning transmission electron microscope to be

$$(\Box{_{{\rm{0}}{\rm{.11}}}}{\rm{ }}{{\rm{K}}_{{\rm{1}}{\rm{.72}}}}{\rm{Na}_{{\rm{0}}{\rm{.17}}})(A}{{\rm{l}}_{{\rm{3}}{\rm{.91}}}}{\rm{ F}}{{\rm{e}}_{{\rm{0}}{\rm{.03}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.11}}}}{\rm{ Al}}{{\rm{l}}_{{\rm{1}}{\rm{.89}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$
and
$$(\Box_{{\rm{1}}{\rm{.90}}}{\rm{N}}{{\rm{a}}_{{\rm{0.06}}}}{{\rm{K}}_{{\rm{0}}{\rm{.04}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.94}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.01}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.94}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.06}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}},$$
 respectively.

The pyrophyllite and muscovite in the Pennsylvania shale likewise occurred only as coexisting coherent to sub-parallel packets as thin as 200 Å, with compositions of

$$(\Box_{{\rm{1}}{\rm{.89}}}{\rm{N}}{{\rm{a}}_{{\rm{0.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.93}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.04}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.02}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.92}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.08}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$
and
$$({\rm{N}}{{\rm{a}}_{{\rm{0}}{\rm{.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{2}}{\rm{.03}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.54}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.24}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.16}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.06}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.09}}}}{\rm{A}}{{\rm{l}}_{{\rm{1}}{\rm{.91}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}.$$
 The textures of both samples were consistent with an equilibrium relationship between pyrophyllite and muscovite. The Pennsylvania sample also contained NH4-rich illite, kaolinite, and an illite-like phase having intermediate Na/K, which collectively imply non-equilibrated low-grade conditions.

The compositions of these coexisting pyrophyllite and muscovite define a solvus with steep limbs and extremely limited solid solution. Illite is a white mica, intermediate in composition between pyrophyllite and muscovite, formed at much lower temperatures than muscovite. These relations show that illite is metastable relative to pyrophyllite + muscovite in all of its diagenetic and low-grade metamorphic occurrences. This further implies that illite precursor phases, such as smectite, are also metastable. The prograde reactions involving smectite, illite, and muscovite are therefore inferred to represent Ostwald-step-rule-like advances through a series of metastable phases toward the equilibrium states attained in the greenschist facies. “Illite crystallinity” can therefore be a measure of reaction progress, for which temperature is only one of several determining factors.

Keywords

Analytical electron microscopyIlliteMuscovitePyrophylliteSolid solutionThermodynamic stabilityTransmission electron microscopy
Type
Research Article
Information
Clays and Clay Minerals , Volume 38 , Issue 3 , June 1990 , pp. 225 - 240
Copyright
Copyright © 1990, The Clay Minerals Society

Footnotes

1

Contribution 467 from the Mineralogical Laboratory, Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109.

References

Aagaard, P. and Helgeson, H. C., 1983 Activity/composition relations among silicates and aqueous solutions: II. Chemical and thermodynamic consequences of ideal mix-ing of atoms on homological sites in montmorillonites, illites, and mixed-layer clays Clays & Clay Minerals 31 207 – 217.CrossRefGoogle Scholar
Ahn, J. H., Peacor, D. R. and Coombs, D. S., 1988 Formation mechanisms of illite, chlorite and mixed-layer illite-chlorite in Triassic volcanogenic sediments from the Southland Syncline, New Zealand Contrib. Mineral. Petrol 99 82 – 89.CrossRefGoogle Scholar
Ahn, J. H., Peacor, D. R. and Essene, E. J., 1985 Coexisting paragonite-phengite in blueschist eclogite: A TEM study Amer. Mineral 70 1193 – 1204.Google Scholar
Baldelli, C., Franceschelli, M., Leoni, L. and Memmi, I., 1989 Ferrimuscovite and celadonite substitutions in muscovite from Fe3+-rich low-grade psammitic rocks (Northern Apennines, Italy) Lithos 23 201 – 208.CrossRefGoogle Scholar
Baxter, S. M. and Peacor, D. R., 1988 TEM observation of polytypism in illite Program and Abstracts, 25th Annual Meeting, Grand Rapids, Michigan 74.Google Scholar
Bucher-Nurminen, K., 1987 A recalibration of the chlorite-biotite-muscovite geobarometer Contrib. Mineral. Petrol 96 519 – 522.CrossRefGoogle Scholar
Burst, J. F. Jr. and Swineford, A., 1959 Post-diagenetic clay mineral environmental relationships in the Gulf Coast Eocene Clays and Clay Minerals, Proc. 6th Natl. Conf., Berkeley, California, 1957 New York Pergamon Press 327 – 341.Google Scholar
Burst, J. F. Jr., 1969 Diagenesis of Gulf Coast clayey sediments and its possible relation to petroleum migration Bull. Amer. Assoc. Petrol. Geol 53 73 – 93.Google Scholar
Burtner, R. I. and Warner, M. A., 1986 Relationship between illite/smectite diagenesis and hydrocarbon generation in Lower Cretaceous Mowry and Skull Creek shales of the northern Rocky Mountain area Clays & Clay Minerals 34 390 – 402.CrossRefGoogle Scholar
Chang, H. K., Mackenzie, F. T. and Schoonmaker, J., 1986 Comparisons between the diagenesis of dioctahedral and trioctahedral smectite, Brazilian offshore basins Clays & Clay Minerals 34 407 123.CrossRefGoogle Scholar
Chermak, J. A. and Rimstidt, J. D., 1989 Estimating the thermodynamic properties (ΔG°f and AH°f) of silicate minerals at 298 K from the sum of polyhedral contributions Amer. Mineral 74 1023 – 1031.Google Scholar
Dunoyer de Segonzac, G., 1970 The transformation of clay minerals during diagenesis and low-grade metarnorphism: A review Sedimentology 15 281 – 346.CrossRefGoogle Scholar
Essene, E. J. and Ferry, J. M., 1982 Geologic thermometry and barometry Characterization of Metarnorphism Through Mineral Equilibria, Reviews in Mineralogy, Vol. 10 Washington, D.C. Mineralogical Society of America 153 – 206.CrossRefGoogle Scholar
Essene, E. J., Daly, J. S., Cliff, R. A. and Yardley, B. W. D., 1989 The current status of thermobarometry in metamorphic rocks Evolution of Metamorphic Belts Boulder, Colorado The Geological Society of America 1 – 44.Google Scholar
Foster, M. D., 1956 Correlation of dioctahedral potassium micas on the basis of their charge relations U.S. Geol. Surv. Bull 1036D 57 – 67.Google Scholar
Franceschelli, M., Mellini, M., Memmi, I. and Ricci, C. A., 1986 Fine-scale chlorite-muscovite association in low-grade metapelites from Nurra (NW Sardinia), and the possible misidentification of metamorphic vermiculite Contrib. Mineral. Petrol 93 137 – 143.CrossRefGoogle Scholar
Franceschelli, M., Mellini, M., Memmi, I. and Ricci, C. A., 1989 Sudoite, a rock-forming mineral in Verrucano of the Northern Apennines (Italy) and the sudoite-chloritoid-pyrophyllite assemblage in prograde metarnorphism Contrib. Mineral. Petrol 101 274 – 279.CrossRefGoogle Scholar
Frey, M., Saunders, J. and Schwander, H., 1988 The mineralogy and metamorphic geology of low-grade metasedi-ments, Northern Range, Trinidad J. Geol. Soc. London 145 563 – 575.CrossRefGoogle Scholar
Frey, M., Teichmueller, M., Teichmueller, R., Mullis, J., Kunze, B., Breitschmid, A., Gruner, U. and Schwizer, B., 1980 Very low grade metarnorphism in external parts of the Central Alps: illite crystallinity, coal rank and fluid inclusion data Eclogae Geologicae Helvetiae 73 173 – 203.Google Scholar
Garrels, R. M., 1984 Montmorillonite/illite stability diagrams Clays & Clay Minerals 32 33 – 48.CrossRefGoogle Scholar
Ghent, E. D., Stout, M. Z. and Ferri, F., 1989 Chloritoid-paragonite-pyrophyllite and stilpnomelane-bearing rocks near Blackwater Mountain, western Rocky Mountains, British Columbia Canad. Mineral 27 59 – 66.Google Scholar
Grim, R. E., 1968 Clay Mineralogy 2nd ed. New York McGraw-Hill 31 – 50.Google Scholar
Helgeson, H. C. and Aagaard, P., 1985 Activity/composition relations among silicates and aqueous solutions: I. Thermodynamics of intrasite mixing and substitutional or-der/disorder in minerals Amer. J. Sci 285 769 – 844.CrossRefGoogle Scholar
Hoffman, J. and Hower, J., 1979 Clay mineral assemblages as low-grade metamorphic geothermometers: Application to thrust faulted disturbed belt of Montana, USA: in Aspects of Diagenesis Soc. Econ. Paleontol. Mineral. Spec. Publ 26 55 – 79.Google Scholar
Hower, J., Eslinger, E. V., Hower, M. E. and Perry, E. A., 1976 Mechanism of burial metarnorphism of argillaceous sediments: 1. Mineralogical and chemical evidence Geol. Soc. Amer. Bull 87 725 – 737.2.0.CO;2>CrossRefGoogle Scholar
Hunziker, J. C., Frey, M., Claver, N., Dollmeyer, R. D., Fried-rickson, H., Flehmig, W., Hochstrasser, K., Roggwiler, P. and Schwander, H., 1986 The evolution of illite to muscovite: Mineralogical and isotopic data from the Grlarus Alps, Switzerland Cont. Mineral. Petrol 92 157 – 180.CrossRefGoogle Scholar
Juster, T. C. and Brown, P. E., 1984 Fluids in pelitic rocks during very low-grade metarnorphism Geol. Soc. Amer. Abstr. Prog 16 553.Google Scholar
Juster, T. C., Brown, P. E. and Bailey, S. W., 1987 NH4-bearing illite in very low grade metamorphic rocks associated with coal, northeastern Pennsylvania Amer. Mineral 72 555 – 565.Google Scholar
Kanehira, K. and Banno, S., 1960 Ferriphengite and ae-girine-jadeite in a crystalline schist of the Iimori District, Kii Peninsula J. Geol. Soc. Japan 66 654 – 659.CrossRefGoogle Scholar
Kisch, H. J., Larsen, G. and Chilingar, G. V., 1983 Mineralogy and petrology of burial diagenesis (burial metamorphism) and incipient metamorphism in clastic rocks Diagenesis in Sediments and Sedimentary Rocks 2 New York Elsevier 289 – 493.Google Scholar
Kisch, H. J. and Frey, M., 1987 Correlation between indicators of very low-grade metamorphism Low Temperature Metamorphism New York Chapman and Hall 227 – 300.Google Scholar
Kubler, B., 1964 Les argiles, indicateurs de metamorphisme Rev. Inst. Franc. Petrol 19 1093 – 1112.Google Scholar
Lee, J. H., Peacor, D. R., Lewis, D. D. and Wintsch, R. P., 1986 Evidence for syntectonic crystallization for the mudstone to slate transition at Lehigh Gap, Pennsylvania, U.S.A. J. Struct. Geol 8 767 – 780.CrossRefGoogle Scholar
Lippmann, F. and Konta, J., 1981 Stability diagrams involving clay minerals 8th Conf. on Clay Mineralogy and Petrology, Teplice 1979 Czechoslovakia Univerzita Karlova, Praha 153 – 171.Google Scholar
Lippmann, F., van Olphen, H. and Veniale, F., 1982 The thermodynamic status of clay minerals Proc. Int. Clay Conf. Bologna, Pavia, 1981 475 – 485.Google Scholar
Massonne, H. J. and Schreyer, W., 1987 Phengite geobarometry based on the limiting assemblage with K-feldspar, phlogopite and quartz Contrib. Mineral. Petrol 96 212 24.CrossRefGoogle Scholar
Mattigod, S. V. and Sposito, G., 1978 Improved method for estimating the standard free energies of formation (ΔGf298, 15) of smectites Geochim. Cosmochim. Acta 42 1753 – 1762.CrossRefGoogle Scholar
May, H. M., Kinniburgh, D. G., Helmke, P. A. and Jackson, M. L., 1986 Aqueous dissolution, solubilities and ther-modynamic stabilities of common aluminosilicate minerals: Kaolinite and smectites Geochim. Cosmochim. Acta 50 1667 – 1677.CrossRefGoogle Scholar
Merino, E. and Ransom, B., 1982 Free energies of formation of illite solid solutions and their compositional dependence Clay & Clay Minerals 30 29 – 39.CrossRefGoogle Scholar
Morse, J. W. and Casey, W. H., 1988 Ostwald processes and mineral paragenesis in sediments Amer. J. Sci 288 537 – 560.CrossRefGoogle Scholar
Nadeau, P. H. and Reynolds, R. C. Jr., 1981 Burial and contact metamorphism in the Mancos Shale Clays & Clay Minerals 29 249 – 259.CrossRefGoogle Scholar
Nriagu, J. O., 1975 Thermodynamical approximations for clay minerals Amer. Mineral 60 834 – 839.Google Scholar
Phillips, G. N., 1987 Metamorphism of the Witwatersrand gold fields: Conditions during peak metamorphism J. Metamorphic Geol 5 307 – 322.CrossRefGoogle Scholar
Prigogine, I. and Defay, R. (1954) Chemical Thermodynamics, translated from the 2nd French ed. by Everett, D. H., Longmans, Green & Co., New York.Google Scholar
Sass, B. M., Rosenberg, P. E. and Kittrick, J. A., 1987 The stability of illite/smectite during diagenesis: An experimental study Geochim. Cosmochim. Acta 51 2103 – 2115.CrossRefGoogle Scholar
Sposito, G., 1986 The polymer model of thermodynamical clay mineral stability Clays & Clay Minerals 34 198 – 203.CrossRefGoogle Scholar
Srodon, J., Eberl, D. D. and Bailey, S. W., 1984 Illite: in Micas Reviews in Mineralogy, Vol. 13 Washington, D.C. Mineralogical Society of America 495 – 544.Google Scholar
Srodon, J., Morgan, D. J., Eslinger, E. V., Eberl, D. D. and Karlinger, M. R., 1986 Chemistry of illite/smectite and end member illite Clays & Clay Minerals 34 368 – 378.CrossRefGoogle Scholar
Stoessell, R. K., 1979 A regular solution site-mixing model for illite Geochim. Cosmochim. Acta 43 1151 – 1159.CrossRefGoogle Scholar
Stoessell, R. K., 1981 Refinements in a site-mixing model for illites: Local electrostatic balance and the quasi-chem-ical approximation Geochim. Cosmochim. Acta 45 1733 – 1741.CrossRefGoogle Scholar
Tardy, Y. and Garrels, R. M., 1974 A method for estimating the Gibbs energies of formation of layer silicates Geochim. Cosmochim. Acta 38 1101 – 1116.CrossRefGoogle Scholar
van der Pluijm, B. A., Lee, J. H. and Peacor, D. R., 1988 Analytical electron microscopy and the problem of potassium diffusion Clays & Clay Minerals 36 498 – 504.CrossRefGoogle Scholar
Velde, B., 1965 Phengite micas: Synthesis, stability and natural occurrence Amer. J. Sci 263 886 – 913.CrossRefGoogle Scholar
Velde, B., 1969 The compositional join muscovite-pyro-phyllite at moderate pressures and temperatures Bull. Soc. Fr. Mineral. Cristallogr 92 360 – 368 (in French).Google Scholar
Weaver, C. E., 1960 Possible uses of clay minerals in search for oil Bull. Amer. Assoc. Petrol. Geol 44 1505 – 1518.Google Scholar
Yau, Y. C., Peacor, D. R., Essene, E. J., Lee, J. H., Kuo, L. C. and Cosca, M. A., 1987 Hydrothermal treatments of smectite, illite, and basalt to 460°C: Composition of natural with hydrothermally formed clay minerals Clays & Clay Minerals 35 241 – 250.CrossRefGoogle Scholar