Compositional variation within some sedimentary chlorites and some comments on their origin

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Authors:Curtis, C. D.; Hughes, C. R.; Whiteman, J. A.; Whittle, C. K.
Author Affiliations:Primary:
Univ. Sheffield, Dep. Geol. and Metall., Sheffield, United Kingdom
Volume Title:Diagenesis and low-temperature metamorphism
Volume Authors:Robinson, D., editor
Source:Mineralogical Magazine, 49 Part 3(352), p.375-386; Diagenesis and low-temperature metamorphism, Bristol, United Kingdom, April 12-13, 1984, edited by D. Robinson. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:1985
Note:In English. 20 refs.; illus. incl. 1 table
Summary:A range of authigenic sedimentary chlorites from sandstones has been studied by analytical transmission electron microscopy. Selected area (single crystal) electron diffraction patterns are of the Ib (β = 90°) polytype confirming the earlier observations of Hayes (1970). TEM analyses show all samples to be relatively rich in both Al and Fe. In the general formula (Mg,Fe,Al)n [Si8-xAlxO20](OH)16, x varies between 1.5 and 2.6; Fe/(Fe + Mg) between 0.47 and 0.83 and n between 10.80 and 11.54. Octahedral Al is close to 3 in this formulation and Fe2+ predominates over Fe3+. Swelling chlorites have significantly different compositions which are consistent with smectite/chlorite interstratifications. The Ib (β = 90°) polytype appears to be stable under conditions of moderate to deep burial. It replaces berthierine and swelling chlorites formed at lower temperatures. As commonly seen in grain coatings, however, it precipitates from porewater; solutes probably being contributed from several mineral decomposition reactions. [R.A.H.]
Subjects:Chamosite; Chlorite; Chlorite group; Clastic rocks; Clay mineralogy; Clinochlore; Diagenesis; Electron diffraction data; Materials; Mineral data; Sandstone; Sedimentary rocks; SEM data; Sheet silicates; Silicates; TEM data; X-ray data
Abstract Numbers:85M/3529
Record ID:1985075827
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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