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The clay mineralogy of some soils derived from a biotite-rich quartz-gabbro in the Strathdon area, Aberdeenshire

Published online by Cambridge University Press:  09 July 2018

M. J. Wilson*
Affiliation:
The Macaulay Institute for Soil Research, Aberdeen

Abstract

Three soils of the Strathdon area, Aberdeenshire, derived from a biotite-rich quartz-gabbro and representing well-drained, imperfectly drained and poorly drained types, were studied. The 50–200 µ fractions contained mainly plagioclase feldspar, amphibole (tremolite and hornblende), biotite and quartz and the following order of relative stability was established: quartz > amphibole > plagioclase feldspar > biotite. In all soils biotite was found to weather to a 14 Å aluminous vermiculite-chlorite with zones of kaolinite. The clay mineral composition of three soils was identical, consisting of trioctahedral vermiculite-chlorite, trioctahedral illite, kaolinite and gibbsite. These minerals originated in various ways through the decomposition of biotite which thus plays a key role in the origin of the clay fraction. It is suggested that the clay mineral constituents of the soils were formed in a regolith predating the last glacial period, and that post glacial soil-forming processes have modified them only slightly.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1967

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