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Some aluminous clinopyroxenes from Vesuvius and Monte Somma, Italy

Published online by Cambridge University Press:  05 July 2018

S. Rahman
S. Rahman*
Affiliation:
Department of Geology, Dacca University, Bangladesh
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Summary

Aluminous Ca-rich clinopyroxenes (5.95-7.63 wt % Al2O3) are next in abundance to leucite in the basic alkaline potassic lavas from Monte Somma and Vesuvius, Italy, and occur as phenocrysts (1 to 7 mm), micropbenocrysts (< 1 mm), and groundmass granules. Zoning of various types is a conspicuous feature in these pyroxenes. Optical and chemical data are presented and a comparison is made between these pyroxenes and similar ones from alkali basalts. It is known from published data that Al2O3 fluctuates strongly in the oscillatory zones of Vesuvian pyroxenes. This can be explained as due to temperature variation in the magma, to magma variation in silica content due to contamination, to oscillations in leucite precipitation, or to a combination of these factors. Of these three factors, oscillations in leucite precipitation, as it appears, would be more effective than the others since it would have a greater control over Si/A1 availability in the magma.

Type
Research Article
Information
Mineralogical Magazine , Volume 40 , Issue 309 , March 1975 , pp. 43 - 52
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1975

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Footnotes

1

Present address: Dept. of Geology, Makerere University, Kampala, Uganda.

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