Evidence for Loss of Protons and Octahedral Iron from Oxidized Biotites and Vermiculites

V. C. Farmer, J. D. Russell, W. J. Mchardy, A. C. D. Newman, J. L. AHLRICHS and J. Y. H. Rimsaite
The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, Scotland
Pedology Department, Rothamsted Experimental Station, Harpenden, Herts.
Purdue University, Lafayette, Indiana, U.S.A.
Geology Survey of Canada, Ottawa, Canada

Summary: Infra-red examination of a weathered biotite and of biotites that have been converted to vermiculites and subsequently oxidized, indicates that oxidation of octahedral ferrous ions to ferric ions is associated with a reversible conversion of hydroxyl ions to oxide ions. Subsequently, in high-iron biotites, there is an irreversible loss of ferric ions from the octahedral layer, resulting in an increased number of dioctahedral sites. Electron microscopy and X-ray diffraction indicate that ejected ferric ions form either amorphous interlayer oxides or, when bromine is used as an oxidant, a crystalline external phase of β-FeOOH. The high refractive index of some oxidized vermiculites is shown to be due largely to submicroscopic iron oxides.

Mineralogical Magazine; June 1971 v. 38; no. 294; p. 121-137; DOI: 10.1180/minmag.1971.038.294.01
© 1971, The Mineralogical Society
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