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The alkali feldspars of the Ardara pluton, Donegal

Published online by Cambridge University Press:  14 March 2018

A. Hall
A. Hall*
Affiliation:
Geology Department, King's College, London, W.C.2
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Summary

The alkali feldspars in the Ardara pluton are microcline- and orthoclase-microperthites. Their compositions have been determined by the 20 X-ray method, both before and after homogenization. The bulk compositions are very rich in potassium as a result of postmagmatic recrystallization of the alkali feldspar. There is no significant variation in either the bulk composition or the composition of the potassic phase in different parts of the intrusion. The structural state of the feldspars has been studied by measurement of 2V and obliquity of the potassic phases, and the reciprocal lattice angles α* and γ* of the potassic and sodic phases in selected crystals. Most of the specimens contain near-maximum microcline, but there is a decrease in the obliquity of the potassic phase at the eastern end of the intrusion. This can be related to the subsequent intrusion of the Main Donegal Granite.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 35 , Issue 273 , March 1966 , pp. 693 - 703
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1966

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