Summary
The principal mineral component in the matrix of the Cochabamba carbonaceous chondrite is a phyllosilicate, which is identified as cronstedtite mainly on the basis of its chemical composition. Its approximate idealized formula is given by M6 Fe 3+0.7 Al0.5Si2.7O10 (OH)8 with M=Fe2+, Fe3+, and Mg in somewhat variable amounts. TEM studies reveal the presence of three polytypes, and show a high degree of stacking disorder parallel to (001) with the displacement vector ±b/3 or ±2b \(\bar 3\). Crumpled amorphous masses in the matrix may contain structural building blocks of phyllosilicates. They, rather than the anhydrous minerals, seem to be the most likely progenitors of cronstedtite. Some constraints on its origin are reviewed. In addition to cronstedtite, observations on some other matrix phases are also reported.
Zusammenfassung
Der Hauptbestandteil der Matrix im kohligen Chondrit Cochabamba ist ein Schichtsilikat, das hauptsächlich aufgrund seiner chemischen Zusammensetzung als Cronstedtit identifiziert wurde. Die idealisierte Formel entspricht ungefähr M6Fe +30.7 Al0.5Si2.7O10(OH)8 mit M=Fe2+, Fe3+ und Mg in wechselnden Mengen. TEM-Untersuchungen zeigen das Vorkommen von drei Modifikationen, sowie einen hohen Grad von Versetzungsfehlern parallel zu (001), mit dem Versetzungsfaktor ±b/3 oder ±2b/3. Deformierte amorphe Aggregate in der Matrix scheinen primitive Bausteine der Schichtsilikate zu sein. Sie (und nicht die wasserfreien Mineralien) dürften das Material darstellen, aus dem Cronstedtit gebildet wurde. Die Bildungsbedingungen von Cronstedtit werden diskutiert. Außerdem wird über Beobachtungen an anderen Matrixmineralien berichtet.
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References
Bunch, T. E., Chang, S., 1978: Carbonaceous chondrite (CM) phyllosilicates: Condensation or alteration origin? Lunar Planet. Sci.9, 134–136 (1978).
Gossner, B., 1936: Über Cronstedtit von Kisbanay. Zbl. Min.A36, 195–201.
Hendricks, S. B., 1938: The crystal structure of nacrite Al2O3·2SiO2·2H2O and the polymorphism of the kaolin minerals. Z. Kristallogr.100, 509–518.
Kallemeyn, G. W., Wasson, J. T., 1979: Unusual chondritic meteorites and clasts: elemental fractionations and relationships to the carbonaceous chondrite groups. Lunar Planet. Sci.10, 644–646.
Kerridge, J. F., 1976: Major element composition of phyllosilicates in the Orgueil carbonaecous meteorite. Earth Planet. Sci. Letts.29, 194–200.
Kerridge, J. F., 1977: Correlation between nickel and sulfur abundances in Orgueil phyllosilicates. Geochim. Cosmochim. Acta41, 1163–1164.
Kurat, G., 1970: Zur Genese des kohligen Materials im Meteoriten von Tieschitz. Earth Planet. Sci. Letts.7, 317–324.
Kurat, G., 1975: Der kohlige Chondrit Lancé: Eine petrologische Analyse der komplexen Genese eines Chondriten. Tschermaks Min. Petr. Mitt.22, 38–78 (1975).
Kurat, G., Kracher, A., 1975: Preliminary report on the Cochabamba carbonaceous chondrite. Meteoritics10, 432–433 (1975).
McSween, H. Y., Richardson, S. M., 1977: The composition of carbonaceous chondrite matrix. Geochim. Cosmochim. Acta41, 1145–1162 (1977).
Müller, W. F., 1976: Low-Fe clinopyroxenes along the join MgSiO3−CaMgSi2O6 in the Allende meteorite. Naturwissenschaften63, 432.
Müller, W. F., Kurat, G., Kracher, A., 1977: Crystal structure and composition of cronstedtite from the Cochabamba carbonaceous chondrite. Meteoritics12, 322.
Nelen, J., Kurat, G., Fredriksson, K., 1975: The Renazzo chondrite — a revaluation. Meteoritics10, 464–465.
Richardson, S. M., 1978: Vein formation in theC1 carbonaceous chondrites. Meteoritics13, 141–159.
Shaw, R., Steadman, R., Pugh, J. D., 1965: Stacking faults in cronstedtite and other kaolin-type silicates. Z. Kristallogr.122, 237–247.
Steadman, R., Nuttall, P. M., 1963: Polymorphism in cronstedtite. Acta Cryst.16, 1–8.
Steadman, R., Nuttall, P. M., 1964: Further polymorphism in cronstedtite. Acta Cryst.17, 404–406.
Steadman, R., 1964: The structures of trioctahedral kaolin-type silicates. Acta Cryst.17, 924–927 (1964).
Wasson, J. T., 1974: Meteorites. Berlin-Heidelberg-New York: Springer.
Wilkening, L. L., 1978: Carbonaceous chondrite material in the solar system. Naturwissenschaften65, 73–79.
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Müller, W.F., Kurat, G. & Kracher, A. Chemical and crystallographic study of cronstedtite in the matrix of the Cochabamba (CM2) carbonaceous chondrite. TMPM Tschermaks Petr. Mitt. 26, 293–304 (1979). https://doi.org/10.1007/BF01089843
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DOI: https://doi.org/10.1007/BF01089843