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Strontian melilite in a nephelinite lava from Etinde, Cameroon

Published online by Cambridge University Press:  05 July 2018

J. G. Fitton  and
D. J. Hughes
J. G. Fitton
Affiliation:
Department of Geology, Edinburgh University, UK
D. J. Hughes
Affiliation:
Department of Geology, Portsmouth Polytechnic, UK
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Abstract

Strontium-rich (up to 16 wt% SrO) melilite occurs as microphenocrysts in a nosean-leucite-nephelinite lava from Etinde, Cameroon. Electron microprobe analyses show that the melilite is very strongly zoned with Sr, Fe, and Na enrichment towards the crystal rims. Sodium melilite and sodium ferrimelilite are the dominant end-member molecules and together account for up to 76 mole%. The crystals are optically negative and strongly birefringent with birefringence ranging from 0.014 in the cores to 0.032 at the crystal rims. Refractive indices measured at the rim of one crystal gave ω = 1.656, ɛ = 1.628. The cell dimensions of strontian melilite are a = 7.765Å, c = 5.054Å.

Type
Research Article
Information
Mineralogical Magazine , Volume 44 , Issue 335 , September 1981 , pp. 261 - 264
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1981

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