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Petrologic evidence for a rhodochrosite precursor of spessartine in coticules of the Venn-Stavelot Massif, Belgium

Published online by Cambridge University Press:  05 July 2018

W. Schreyer
Affiliation:
Institut für Mineralogie, Ruhr-Universität Bochum, Germany
H.-J. Bernhardt
Affiliation:
Institut für Mineralogie, Ruhr-Universität Bochum, Germany
O. Medenbach
Affiliation:
Institut für Mineralogie, Ruhr-Universität Bochum, Germany

Abstract

Minute CaMg-bearing rhodochrosite inclusions were discovered in spessartine crystals of small coticule globules enclosed within redschists that form the country rock of the famous coticule bands of Belgium. This points to a former metamorphic reaction relationship between the two minerals, such as rhodochrosite + pyrophyllite = spessartine + quartz + CO2 + H2O. The coexistence of spessartine with Mg-chlorite in the coticule globule could also indicate more complex reactions such as rhodochrosite + sudoite + quartz = spessartine + Mg-chlorite + CO2 + H2O. Our finding casts some doubt on the suggestion by Kramm (1976) that spessartine formed from Mn-montmorillonite in previously glassy volcanic tufts.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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