Letter | Published:

Winchite and the actinolite–glaucophane miscibility gap

Nature volume 296, pages 731732 (22 April 1982) | Download Citation

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Abstract

Leake et al.1 have recently emphasized the apparent scarcity of winchite s.l., NaCa(Mg, Fe2+)4(Al, Fe3+) [Si8O22/(OH)2] (ref. 2), an amphibole intermediate in composition between the glaucophane–riebeckite series of high-pressure blueschists and the tremolite–actinolite series of lower-pressure greenschists. The rarity of winchite is considered consistent with the existence of a miscibility gap3,4 between these two amphibole series at the metamorphic P–T conditions normally attained in nature. Here we present optical and X-ray properties of Mg- and Al-rich winchite from Venezuela and draw attention to several other recent winchite analyses. In fact, as Schliestedt's5 new data on co-existing sodic and calcic amphiboles in blueschists show, only the present Mg–Al-rich winchite definitely lies within the above miscibility gap.

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Author notes

    • A. Rudolph

    Present address: Im Bungert 12, 4300 Essen, FRG.

Affiliations

  1. Institut für Mineralogie, Ruhr-Universität Bochum, D-4360 Bochum, FRG

    • W. V. Maresch
    • , O. Medenbach
    •  & A. Rudolph

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DOI

https://doi.org/10.1038/296731a0

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