A Mössbauer Study of Biotite Weathering

C. M. Rice and J. M. Williams1
Department of Geology, University of Sheffield, Sheffield, England
Department of Physics, University of Sheffield, Sheffield, England
1Present address: Physik-Department der Technischen Hochschule München, 8 München 2, Arcisstrasse 21, Germany.

Summary: Fresh and weathered biotites have been studied using Mössbauer, chemical, and X-ray analytical techniques. In the Mössbauer spectra the complete interference of both low-spin ferric lines by one of the high-spin ferrous lines and the existence of high-spin ferric iron in the weathered biotite has been demonstrated. In view of this interference, which appears to be common, allowances must be made in spectral interpretation if chemical analysis reveals ferric iron to be present in detectable amounts. Hypothetical extension of the weathering trends observed suggests that high-spin ferric iron is the only stable iron species in the end product.

During weathering marked loss of ferrous iron occurs, whereas the ferric iron content remains approximately constant. As a result of the instability of ferrous iron in the weathering environment there is a significant rearrangement of the octahedral layer.

Mineralogical Magazine; June 1969 v. 37; no. 286; p. 210-215; DOI: 10.1180/minmag.1969.037.286.08
© 1969, The Mineralogical Society
Mineralogical Society (www.minersoc.org)