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Phase relations of aenigmatite minerals in a syenitic ejectum, wonchi volcano, Ethiopia

Published online by Cambridge University Press:  05 July 2018

Mario Gaeta  and
Annibale Mottana
Mario Gaeta
Affiliation:
Dipartimento di Scienze della Terra, Università, di Roma ‘La Sapienza’, Piazzale A. Moro, 5, I-00185 Roma RM, Italy
Annibale Mottana
Affiliation:
Dipartimento di Scienze della Terra, Università, di Roma ‘La Sapienza’, Piazzale A. Moro, 5, I-00185 Roma RM, Italy
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Abstract

Wonchi volcano (Ethiopia) is the second locality for wilkinsonite, the new mineral related to aenigmatite via the coupled substitution 2Fe3+ = TiFe2+. Wilkinsonite occurs as relics surrounded by rims of riebeckite and biotite in a syenitic ejectum which also contains microphenocrysts of aenigmatite. The two minerals do not represent an equilibrium pair. They both formed in the magma chamber under plutonic to hypabyssal conditions, but during two following stages of crystallisation separated by a major drop in ƒO2 conditions.

Keywords

aenigmatitewilkinsonitesyenitic ejectumWonchi volcanoEthiopia
Type
Mineralogy
Information
Mineralogical Magazine , Volume 55 , Issue 381 , December 1991 , pp. 529 - 534
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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