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Chemical changes during the alteration of micas

Published online by Cambridge University Press:  09 July 2018

A. C. D. Newman  and
G. Brown
A. C. D. Newman
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts
G. Brown
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts
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Abstract

Di- and trioctahedral micas were altered to vermiculite-like minerals by extracting the K with sodium tetraphenylboron. Chemical analysis of original and altered micas shows that loss of K is accompanied by an increased loss on ignition, oxidation of some Fe2+ to Fe3+, loss of divalent octahedral cations, mainly Mg2+, loss of OH− (or sorption of H+) and decrease in net negative charge.

The following reactions are suggested to explain these changes: (1) replacement of K by Na at interlayer sites; (2) release of structural OH− ions exposed by replacement of K, which decreases the negative charge and allows the structure to expand and more K to be replaced; (3) oxidation of Fe2+ ions by the reaction

4Fe2+ + 4 structural (OH−) + O2 → 4Fe3+ + 4 structural (O2−) + 2H2O;

and (4) release of divalent octahedral ions, possibly through some of the holes left when structural OH− is lost.

The wide implications of these proposals are discussed.

Type
Research Article
Information
Clay Minerals , Volume 6 , Issue 4 , December 1966 , pp. 297 - 310
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1966

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