Crystal structure and cation ordering of piemontite

W. A. Dollase

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Research Article| June 01, 1969

Crystal structure and cation ordering of piemontite

W. A. Dollase

Department of Geology, University of California, Los Angeles 90024.

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Author and Article Information

W. A. Dollase

Department of Geology, University of California, Los Angeles 90024.

Publisher: Mineralogical Society of America

Received: 29 Aug 1968

Accepted: 09 Jan 1969

First Online: 06 Jul 2018

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (1969) 54 (5-6): 710–717.

Abstract

The crystal structure of the Mn³⁺-bearing epidote, piemontite, has been refined. For a crystal of composition, Cz₆₅Pm₂₄Ps₁₁, refinement of the occupancies cf the two large, nominally calcium sites and the three non-equivalent octahedral sites, gives:

({Ca}_{1.00}) ({Ca}_{0.87} {Sr}_{0.18}) ({Al}_{0.80} M_{0.20}) ({Al}_{1.00}) ({Al}_{0.17} M_{0.83}) {Si}_{3} O_{12} OH,

where M = Mn_0.7Fe_0.3. All of the (Mn, Fe) substitution for A1 occurs in one of the two nonequivalent chains of edge-sharing octahedra. In the substituted chain, which is topologically identical with that found in the olivine structure, the larger M(3) site (symmetry-m) lying on the edge of the chain, contains most of the (Mn,Fe) with lesser amounts in the smaller M(l) site (symmetry-T) which forms the core of the chain.