Coulsellite, CaNa3AlMg3F14, a rhombohedral pyrochlore with 1:3 ordering in both A and B sites, from the Cleveland Mine, Tasmania, Australia

William Mumme, Ian Grey, W Birch, Allan Pring, Catherine Bougerol, N Wilson

    Research output: Contribution to journalArticle

    6 Citations (Scopus)

    Abstract

    Coulsellite, CaNa3AlMg3F14, from the Cleveland tin mine at Luina, western Tasmania, has a rhombohedral distortion of the cubic pyrochlore A2B2X6Y structure, with a = 7.1756(1) Å, α = 59.867(1)°, space group R3̄m, Z = 1. The corresponding hexagonal cell parameters are a = 7.1620(1) Å, c = 17.5972(3) Å. The crystals are multiply twinned about threefold axes of the pseudocubic cell. The structure was determined using X-ray data collected on a twinned crystal and refined to Robs = 0.027 for 452 observed reflections with I > 2σ(I). The structure is possibly unique among published structures of pyrochlore-like minerals in having full 1:3 ordering of Ca:Na in the A sites and Al:Mg in the B sites. Transmission electron photomicrographs show a nanodomain structure due to twinning on a scale of ∼5 nm.

    Original languageEnglish
    Pages (from-to)736-740
    Number of pages5
    JournalAmerican Mineralogist
    Volume95
    Issue number5-6
    DOIs
    Publication statusPublished - May 2010

    Keywords

    • 1:3 cation ordering in CaNa AlMg F
    • New fluoride mineral
    • Rhombohedral pyrochlore
    • Structure determination

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