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The conditions of metamorphism of a grossular-wollastonite-vesuvianite skarn from the Omey Granite, Connemara, Western Ireland, with special reference to the chemistry of vesuvianite.

Ahmed-Said, Y. and Leake, Bernard E. 1996. The conditions of metamorphism of a grossular-wollastonite-vesuvianite skarn from the Omey Granite, Connemara, Western Ireland, with special reference to the chemistry of vesuvianite. Mineralogical Magazine 60 (401) , pp. 541-550. 10.1180/minmag.1996.060.401.01

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Abstract

The Fountain Hill skarn, which was produced by thermal metamorphism of impure limestone in the Omey Granite aureole, consists of wollastonite, calcite, grossular-andradite garnet, diopside, B-free vesuvianite and small amounts of albite, K-feldspar and quartz. Zoning in vesuvianite is, overall, independent of birefringence but oscillatory concentric zoning in the mineral is controlled mainly by Ti. In addition to extensive within-site substitutions (e.g. F for OH in the OH-sites, Fe2+ for Mg, Fe3+ for Al, Ti for Al etc. in the Y-sites), there are significant cross-site combined substitutions involving Y-X and Y-Z but not X-Z sites so that ideal solution models for this mineral are not applicable. The thermodynamic mole fraction of Hoisch (1985) is modified to account for the excess of the ΣY cations in the Y sites and can be applied to both B-bearing and B-free vesuvianites. Using the thermodynamic dataset of Holland and Powell (1990) and taking into account the existence of andalusite, sillimanite and corundum in associated pelites, leads to the conclusion that the metamorphic conditions were about 640±20°C and 3.3±0.3 kb at 0.15±0.05 XCO2 .

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Mineralogical Society
ISSN: 0026-461X
Last Modified: 09 Jul 2020 15:01
URI: http://orca.cf.ac.uk/id/eprint/133067

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