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Study of minerals from the pegmatites of the Nellore mica-belt, Andhra Pradesh, India Part I. Microcline perthites

Published online by Cambridge University Press:  05 July 2018

V. R. R. M. Babu
V. R. R. M. Babu*
Affiliation:
Department of Geology, Andhra University, Waltair
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Summary

The obliquity values of microcline perthites are nearer to maximum microcline type, indicating that they have less than 10% Ab in their lattices, apart from exsolved albite. The perthites are classified based on form as stringlet, string, film, vein, and replacement types. It is concluded that stringlet and string perthites are formed by exsolution along contraction cracks, followed by film as a result of decrease in rate of cooling and increase in water vapour content of the pegmatites, whereas vein and replacement perthites are formed last, by replacement when the pegmatites crystallized in a closed system. Based on the chemical composition of microcline perthites, a temperature of 600 °C is arrived at for unmixing of feldspar to give rise to microcline perthite.

Type
Research Article
Information
Mineralogical Magazine , Volume 37 , Issue 285 , March 1969 , pp. 135 - 139
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1969

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