Letter | Published:

Exceptionally Calcic Pyralspite from South African Kyanite Eclogite

Nature volume 212, pages 6869 (01 October 1966) | Download Citation

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Abstract

PYRALSPITE garnets with C (=Ca/Ca+Mg+Mn+Fe2+)> 0.35 are rare. Some authors1 postulate a miscibility gap between garnets of composition C < 0.35 and the ugrandite series with C > 0.70. The alternative, that garnets with 0.35<C<0.70 are stable but crystallize, under suitable physical conditions, only from rarely encountered silica-poor bulk compositions, has also been suggested2. This hypothesis is supported by the synthesis of a complete series of garnets (C = 0−1.0) between pyrope and grossularite at 30 kbars and 1,200° C (ref. 3). The synthetic garnets with C values between 0.5 and 0.7 are of particular interest because at 30 kbars and 1,600° C these compositions crystallize as clinopyroxene solid solutions4, while the paragenesis clinopyroxene + corundum is a third possibility. The essential relationships are illustrated by the equations:

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Affiliations

  1. Grant Institute of Geology, University of Edinburgh.

    • M. J. O'HARA
    •  & E. L. P. MERCY

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https://doi.org/10.1038/212068b0

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