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Strontian fluoro-magnesiohastingsite in Alban Hills lavas (Central Italy): constraints on crystallization conditions

Published online by Cambridge University Press:  05 July 2018

M. Gaeta*
Affiliation:
Dipartimento di Scienze della Terra, Universita̒ degli Studi ‘La Sapienza’, P. le Aldo Moro 5, I-00185 Roma, Italy
C. Freda
Affiliation:
Dipartimento di Scienze della Terra, Universita̒ degli Studi ‘La Sapienza’, P. le Aldo Moro 5, I-00185 Roma, Italy

Abstract

A magmatic calcic amphibole (M4Ca≥1.50) characterized by large Sr and F contents (SrO>1 wt.%, F>2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in the A sites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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