Zr-rich Garnet and Zr- and Th-rich Perovskite from the Polino Carbonatite, Italy

L. Lupini, C. T. Williams and A. R. Woolley
Dipartimento di Scienze della Terra, Universita di Perugia, Piazza Universita, 06100 Perugia, Italy
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 Fe3+ 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.

Keywords: garnet • perovskite • zirconium • thorium • carbonatite • Italy

Mineralogical Magazine; December 1992 v. 56; no. 385; p. 581-586; DOI: 10.1180/minmag.1992.056.385.14
© 1992, The Mineralogical Society
Mineralogical Society (www.minersoc.org)