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Licensed Unlicensed Requires Authentication Published by De Gruyter March 26, 2015

Triclinic liddicoatite and elbaite in growth sectors of tourmaline from Madagascar

  • Mizuhiko Akizuki , Takahiro Kuribayashi EMAIL logo , Toshiro Nagase and Arashi Kitakaze
From the journal American Mineralogist

Abstract

Crystals of liddicoatite-elbaite tourmaline from a pegmatite in Jochy, Madagascar are composed of o{021̄1}, r{101̄1}, c{0001}, a{112̄̄0}, and m{101̄0} sectors, which correspond to the prominent crystal faces, respectively. Therefore, the sectors were produced during growth, not by strain after growth. The o, m, and r sectors of one specimen are biaxial between crossed polars [2V(-) = 30°, 20°, and 15°, respectively] and triclinic, as indicated by X-ray diffraction. The a sector is optically biaxial and orthorhombic. The c sector is optically uniaxial and essentially trigonal as indicated by single-crystal X-ray diffraction. The o, r, and c sectors are of liddicoatite component, whereas the a sector of the one specimen corresponds to fluor-elbaite. Another crystal specimen comprises a and m sectors, which are polysynthetically twinned, resulting in striations parallel to the c axis on the prism faces, and of liddicoatite. All five sectors have vacancies in the X-site (Ca, Na, ⃞ ).

Received: 1999-11-18
Accepted: 2000-10-29
Published Online: 2015-3-26
Published in Print: 2001-2-1

© 2015 by Walter de Gruyter Berlin/Boston

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