Comparison of sedimentary chlorite compositions by X-ray diffraction and analytical TEM

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Authors:Whittle, C. K.
Author Affiliations:Primary:
Univ. Sheffield, Dep. Geol., Sheffield, United Kingdom
Volume Title:Clay Minerals
Source:Clay Minerals, 21(5), p.937-947. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1986
Note:In English. 25 refs.; illus. incl. 4 tables
Summary:Authigenic chlorites occurring as pore linings in reservoir sandstones have been investigated by XRD and TEM/EDAX. Both methods identified the Ib (β = 90°) polytype. TEM/EDAX analyses suggest that the chlorites are Al-rich, Mg-chamosites with Fe/(Fe + Mg) > 0·47. Octahedral Al exceeds tetrahedral Al, resulting in octahedral totals of less than the theoretical 12·0. Compositions were estimated from XRD data using the equations after Brindley (1961) and Shirozu (1958). XRD-determined compositions are relatively enriched in tetrahedral Al and octahedral Mg, giving Fe/(Fe + Mg) > 0·4 and suggesting that the chlorites are Al-rich clinochlores. XRD estimates plot in the same compositional area as authigenic Ib (β = 90°) chlorites of Hayes (1970), but also within the compositional area of metamorphic chlorites. Caution should be exercised when estimating the composition of sedimentary chlorites by XRD as results appear to overestimate Mg content because of the excess of octahedral R3+ over tetrahedral R3+. [D.J.M.]
Subjects:Authigenic minerals; Chlorite; Chlorite group; Clay mineralogy; Clay minerals; Mineral data; Minerals; Sheet silicates; Silicates; TEM data; X-ray data
Abstract Numbers:87M/4722
Record ID:1987055319
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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