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The petrology and chemical composition of a tholeiite sill on Schaapkraal 68JT, Lydenburg District, Transvaal, South Africa

Published online by Cambridge University Press:  05 July 2018

C. Frick
C. Frick*
Affiliation:
Department of Geology, University of Pretoria
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Summary

A glass-bearing dolerite, which consists of orthopyroxene phenocrysts (γ 1·689, α 1·678, β 1·680, 2Vα 81°, S.G. 3·35) and a glassy mesostasis (n 1·568, S.G. 3·25), is described petrologically. Three new chemical analyses are given. From the petrological and chemical data it can be concluded that the orthopyroxene formed under intratelluric conditions and probably under high pressure. According to the recalculated chemical analysis of the orthopyroxene 0·22 Al3+ is in the Y position and much less Al3+ in the Z position. The chemical analysis of the residual glass is compared with similar residual glasses, and it shows that iron enrichment characterizes the earlier stages of crystallization differentiation, whereas the later stages are marked by an increase in Si4+, K+, and Na+.

Type
Research Article
Information
Mineralogical Magazine , Volume 37 , Issue 292 , December 1970 , pp. 909 - 915
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1970

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