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Authigenic chlorites: problems with chemical analysis and structural formula calculations

Published online by Cambridge University Press:  09 July 2018

C. D. Curtis ,
B. J. Ireland ,
J. A. Whiteman ,
R. Mulvaney  and
C. K. Whittle
C. D. Curtis
Affiliation:
Departments of Geology and Metallurgy, The University of Sheffield, Mappin Street, Sheffield S10 2TN
B. J. Ireland
Affiliation:
Departments of Geology and Metallurgy, The University of Sheffield, Mappin Street, Sheffield S10 2TN
J. A. Whiteman
Affiliation:
Departments of Geology and Metallurgy, The University of Sheffield, Mappin Street, Sheffield S10 2TN
R. Mulvaney
Affiliation:
Departments of Geology and Metallurgy, The University of Sheffield, Mappin Street, Sheffield S10 2TN
C. K. Whittle
Affiliation:
Departments of Geology and Metallurgy, The University of Sheffield, Mappin Street, Sheffield S10 2TN
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Abstract

Analytical transmission electron microscopy was applied to some authigenic chlorites occurring as grain coatings in sandstones. Compositional variation proved to be relatively slight: all were magnesian chamosites. The coating chlorites were often intimately mixed with extremely fine-grained (0·01–0·2 µm) hematite but analytical ‘contamination’ was avoided because of the very high resolution of both observation (spot location) and analysis. One example of a water-sensitive (‘swelling chlorite’) coating was also studied. This proved to have a very much more variable composition even within a single section. The coating appeared to include both chloritic and vermiculitic components. The effect of this on structural formulae is discussed and a model proposed in which the ‘talc’ layer may be common to both components.

Type
Research Article
Information
Clay Minerals , Volume 19 , Issue 3 , June 1984 , pp. 471 - 481
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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