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A Golden-Colored, Ferri-Nickel Chloritic Mineral from Morro do Niquel, Minas Gerais, Brazil

Published online by Cambridge University Press:  01 July 2024

G. W. Brindley  and
Jefferson Vieira de Souza
G. W. Brindley
Affiliation:
Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Jefferson Vieira de Souza
Affiliation:
Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Abstract

A golden-colored, flaky mineral from Morro do Niquel, Minas Gerais, Brazil, gives an X-ray diffraction pattern of a IIb chlorite polytype, with basal spacing 14·21 ± 0·02 Å and b = 9·23 Å. Thermogravimetric analysis shows a progressive weight (water) loss up to 500°C, followed by a rapid weight loss corresponding to dehydroxylation of the interlayer material and a slower weight loss due to dehydroxylation of the 2:1 layer. The structural formula derived from the chemical analysis on the basis of O10 (OH)8, or total cation valence of +28, shows 5·3 total octahedral cations, i.e. probably 2·3 in the interlayers where normally 3 cations are found. This deficiency together with the appreciable loss of water below 500°C suggests a partially vermiculitized interlayer. A new method for deriving the interlayer composition gives R1·67(OH)4·08(H2O)0·59, and a ratio (OH + H2O)/R = 2·80, which approaches that of a dioctahedral interlayer and is consistent with a predominance of R3+ ions. The mineral may resemble the golden, vermiculitized biotite described by Walker and others.

Type
Research Article
Information
Clays and Clay Minerals , Volume 23 , Issue 1 , February 1975 , pp. 11 - 15
Copyright
Copyright © 1975, The Clay Minerals Society

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