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Weathering microenvironments on feldspar surfaces: implications for understanding fluid-mineral reactions in soils

Published online by Cambridge University Press:  05 July 2018

M. R. Lee ,
D. J. Brown ,
M. E. Hodson ,
M. Mackenzie  and
C. L. Smith
M. R. Lee*
Affiliation:
Department of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, Uk
D. J. Brown
Affiliation:
Department of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, Uk
M. E. Hodson
Affiliation:
Department of Soil Science, School of Human and Environmental Sciences, The University of Reading, Whiteknights, Reading RG6 6DW, Uk
M. Mackenzie
Affiliation:
Department of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow G12 8QQ, Uk
C. L. Smith
Affiliation:
Department of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, Uk
*
*E-mail: m.lee@ges.gla.ac.uk
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Abstract

The mechanisms by which coatings develop on weathered grain surfaces, and their potential impact on rates of fluid-mineral interaction, have been investigated by examining feldspars from a 1.1 ky old soil in the Glen Feshie chronosequence, Scottish highlands. Using the focused ion beam technique, electron-transparent foils for characterization by transmission electron microscopy were cut from selected parts of grain surfaces. Some parts were bare whereas others had accumulations, a few micrometres thick, of weathering products, often mixed with mineral and microbial debris. Feldspar exposed at bare grain surfaces is crystalline throughout and so there is no evidence for the presence of the amorphous ‘leached layers’ that typically form in acid-dissolution experiments and have been described from some natural weathering contexts. The weathering products comprise sub-urn thick crystallites of an Fe-K aluminosilicate, probably smectite, that have grown within an amorphous and probably organic-rich matrix. There is also evidence for crystallization of clays having been mediated by fungal hyphae. Coatings formed within Glen Feshie soils after ∼1.1 ky are insufficiently continuous or impermeable to slow rates of fluid-feldspar reactions, but provide valuable insights into the complex weathering microenvironments on debris and microbe-covered mineral surfaces.

Keywords

alkali feldsparTEMsmectiteweathering
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 6 , December 2008 , pp. 1319 - 1328
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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Footnotes

†

Present address: Institut für Mineralogie, Westfälische, Wilhelms-Universität Münster, Corrensstrasse 24, 48149 Münster, Germany

§

Present address: Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK

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