Omsite, (Ni,Cu)_2Fe^(3+)(OH)_6[Sb(OH)_6], a new member of the cualstibite group from Oms, France
Abstract
Omsite (IMA 2012-025) is a new mineral from the Correc d'en Llinassos, Oms, Pyrénées-Orientales Department, France. It occurs as bright yellow to amber yellow discoidal tablets, flattened on {001}, which form rosettes typically 50–100 μm in diameter. Omsite generally crystallizes on siderite without associated supergene minerals; it occurs less commonly with glaukosphaerite. Crystals have a vitreous to resinous lustre, and are transparent to translucent. Omsite is not fluorescent in either short-wave or long-wave ultraviolet light. It has an estimated hardness of 3 on the Mohs' scale, is brittle with an irregular fracture, and has one poor cleavage on {001}. The calculated density is 3.378 g cm^(−3). Crystals are uniaxial (−), with indices of refraction of ω = 1.728(3) and ε = 1.66(1), measured in white light. Pleochroism is ω = orange-yellow, ε = pale orange-yellow; ω > ε. The empirical formula [based on 12 (OH + Cl) p.f.u.] is (Ni^(2+)_(1.099)Cu^(2+)_(0.665)Mg_(0.107)Fe^(3+)_(0.045) _(Σ1.916)Fe^(3+)_(1.000)(Sb^(5+)_(0.947)As_(0.072)Na_(0.029)_(Σ1.048)OH_(11.967)Cl_(0.033). Omsite crystallizes in space group P3İ, with unit-cell parameters ɑ = 5.3506(8), c = 19.5802(15) Å, V = 485.46(10) Å3 and Z = 2 determined by single crystal X-ray diffraction. The five strongest lines in the X-ray powder diffraction pattern [d in Å, (I_(rel)), (hkl)] are as follows: 4.901, (100), (004); 4.575, (83), (011); 2.3539, (81), (114İ); 1.8079, (48), (118İ); 3.781, (34), (103). The crystal structure was solved to R_1 = 0.0896 for 356 observed reflections [F_o>4σF_o] and 0.1018 for all the 469 unique reflections. Omsite is a layered double hydroxide (LDH) mineral, with a topology consistent with members of the hydrotalcite supergroup and cualstibite group.
Additional Information
© 2012 The Mineralogical Society. Received 5 July 2012; Accepted 13 August 2012; Associate Editor: G. Diego Gatta. Referees Gunnar Raade, Uwe Kolitsch and Andy Christy are thanked for their helpful comments on the manuscript. Part of this study was funded by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County. The microprobe analyses were supported by a grant to the California Institute of Technology from the Northern California Mineralogical Association. Jean-Marc Johannet is thanked for the colour photography.Attached Files
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Additional details
- Eprint ID
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- CaltechAUTHORS:20130122-091723431
- John Jago Trelawney Endowment
- Northern California Mineralogical Association
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2013-01-22Created from EPrint's datestamp field
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2021-11-09Created from EPrint's last_modified field