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Zr-rich garnet and Zr- and Th-rich perovskite from the Polino carbonatite, Italy

Published online by Cambridge University Press:  05 July 2018

L. Lupini
Affiliation:
Dipartimento di Scienze della Terra, Universita di Perugia, Piazza Universita, 06100 Perugia, Italy
C. T. Williams
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K.
A. R. Woolley
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K.

Abstract

Th- and Zr-bearing perovskite and Zr-rich Ti garnet are described from the Polino calcite carbonatite, Italy. The garnets contain 6.05-7.50 wt.% ZrO2 in cores and up to 15.80 wt.% in rims. Silicon is low in these garnets and substantial Al and Fe 3+ has been assigned to the tetrahedral sites. A strong correlation of Si with Zr from published data suggests the possibility that some Zr may also be tetrahedrally coordinated. However, the chemistry alone does not constrain the site distribution of Fe, Ti, Zr and Mg unambiguously. The perovskites are very unusual in containing 2.81-3.27 wt.% ZrO2 and 1.48-1.71 wt.% ThO2. For comparison, new analyses are presented of the zirconium garnet kimzeyite and coexisting perovskite from the type locality at Magnet Cove.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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