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The transformation of groutite (α-MnOOH) into pyrolusite (MnO2)

Published online by Cambridge University Press:  14 March 2018

J. Lima-De-Faria  and
A. Lopes-Vieira
J. Lima-De-Faria
Affiliation:
Laboratório de T.F.Q.M.P., Junta de Investigações do Ultramar, Lisbon, Portugal
A. Lopes-Vieira
Affiliation:
Laboratório de T.F.Q.M.P., Junta de Investigações do Ultramar, Lisbon, Portugal
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Summary

The transformation of groutite (α-MnOOH) by heating has been studied at 300° C in air, by single-crystal and powder X-ray methods. At this temperature groutite transforms topotactically into pyrolusite (MnO2), the a, b, and c axes of groutite becoming respectively the a, b, and c axes of pyrolusite (in pyrolusite b = a). At various stages of the transformation other weak and diffuse spots were observed on X-ray oscillation photographs, which could not be ascribed to pyrolusite. Some of these extra spots fit well to an α-Mn2O3 structure (isostructural with hematite), with c 14·3 and a 4·9 Å; the other few spots could not be identified.

The transformation of α-MnOOH into MnO2 is explained by a homogeneous mechanism, with migration of protons and electrons to the crystal surface. A detailed interpretation of this mechanism is presented on the basis of the close-packing characteristics of these two structures.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 33 , Issue 266 , September 1964 , pp. 1024 - 1031
Copyright
Copyright © 1964, The Mineralogical Society

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