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Thermal transformation of lepidomelane

Published online by Cambridge University Press:  05 July 2018

Mizuhiko Akizuki ,
Hiroshi Konno ,
Noriyoshi Yamauchi  and
Ichiro Sunagawa
Mizuhiko Akizuki
Affiliation:
Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, 980 Japan
Hiroshi Konno
Affiliation:
Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, 980 Japan
Noriyoshi Yamauchi
Affiliation:
Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, 980 Japan
Ichiro Sunagawa
Affiliation:
Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, 980 Japan
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Summary

Lepidomelane, an iron-rich biotite, was heated in air or in vacuum, or by electron bombardment, and the processes of dehydration and transformation were studied by means of X-ray diffractometry, optical microscopy, and electron microscopy. By heat treatment, vacancies are at first formed by the evaporation of water molecules and alkali ions, and they move and condense to form holes, which act as preferential nucleation sites for new phases. Other preferential sites are edges of exposed silicate sheets along microcracks, and these are decorated by a newly formed maghemite- like mineral whose a is 10.20 Å (on a hexagonal cell), so that the sites can be clearly seen even under the reflection microscope. By heating at higher temperatures or prolonged heating, various phases, olivine, hematite, magnetite, and leucite are formed, depending upon the conditions of dehydration.

Type
Research Article
Information
Mineralogical Magazine , Volume 40 , Issue 311 , September 1975 , pp. 239 - 245
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1975

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References

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