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Bobmeyerite, a new mineral from Tiger, Arizona, USA, structurally related to cerchiaraite and ashburtonite

Kampf, A. R. and Pluth, J. J. and Chen, Y. S. and Roberts, A. C. and Housley, R. M. (2013) Bobmeyerite, a new mineral from Tiger, Arizona, USA, structurally related to cerchiaraite and ashburtonite. Mineralogical Magazine, 77 (1). pp. 81-91. ISSN 0026-461X. doi:10.1180/minmag.2013.077.1.08.

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Bobmeyerite, Pb_4(Al_(3)Cu)(Si_(4)O_12)(S_(0.5)Si_(0.5)O_4)(OH)_(7)Cl(H_(2)O)_3, is a new mineral from the Mammoth - Saint Anthony mine, Tiger, Pinal County, Arizona, USA. It occurs in an oxidation zone assemblage attributed to progressive alteration and crystallization in a closed system. Other minerals in this assemblage include atacamite, caledonite, cerussite, connellite, diaboleite, fluorite, georgerobinsonite, hematite, leadhillite, matlockite, murdochite, phosgenite, pinalite, quartz, wulfenite and yedlinite. Bobmeyerite occurs as colourless to white or cream-coloured needles, up to 300 mm in length, that taper to sharp points. The streak is white and the lustre is adamantine, dull or silky. Bobmeyerite is not fluorescent. The hardness could not be determined, the tenacity is brittle and no cleavage was observed. The calculated density is 4.381 g cm^(-3). Bobmeyerite is biaxial (-) with a ≈ b = 1.759(2), γ = 1.756(2) (white light), it is not pleochroic; the orientation is X = c; Y or Z = a or b. Electron-microprobe analyses provided the empirical formula Pb_(3.80)Ca_(0.04)Al_(3.04) Cu^(2+)_(0.96)Cr^(3+)_(0.13)Si_(4.40)S_(0.58)O_(24.43) Cl_(1.05)F_(0.52)H_(11.83). Bobmeyerite is orthorhombic (pseudotetragonal), Pnnm with unit-cell parameters a = 13.969(9), b = 14.243(10), c = 5.893(4) Å, V = 1172.5(1.4) Å 3 and Z = 2. The nine strongest lines in the X-ray powder diffraction pattern, listed as [d_(obs)(Å )(I)(hkl)], are as follows: 10.051(35)(110); 5.474(54)(011,101); 5.011(35)(220); 4.333(43)(121,211); 3.545(34)(040,400); 3.278(77)(330,231,321); 2.9656(88)(141,002,411); 2.5485(93)(051,222,501); 1.873(39)(multiple). Bobmeyerite has the same structural framework as cerchiaraite and ashburtonite. In the structure, which refined to R_1 = 0.079 for 1057 reflections with F > 4σF, SiO_4 tetrahedra share corners to form four-membered Si_(4)O_12 rings centred on the c axis. The rings are linked by chains of edge-sharing AlO_6 octahedra running parallel to [001]. The framework thereby created contains large channels, running parallel to [001]. The Cl site is centred on the c axis alternating along [001] with the Si_(4)O_12 rings. Two non-equivalent Pb atoms are positioned around the periphery of the channels. Both are elevencoordinate, bonding to the Cl atom on the c axis, to eight O atoms in the framework and to two O (H_(2)O) sites in the channel. The Pb atoms are off-centre in these coordinations, as is typical of Pb^2+ with stereo-active lone-electron pairs. A (S, Si, Cr)O_4 group is presumed to be disordered in the channel. The name honours Robert (Bob) Owen Meyer, one of the discoverers of the new mineral.

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Kampf, A. R.0000-0001-8084-2563
Additional Information:© 2013 The Mineralogical Society. Received 2 October 2012; Accepted 6 January 2013. Reviewers Peter Leverett and Mark Cooper and Editorial Board Member Stuart Mills are thanked for their constructive comments on the manuscript. Bob Meyer, Joe Ruiz and Brent Thorne provided specimens of the new species. The structure data collection was carried out at GSECARS and ChemMatCARS (CARS = Consortium for Advanced Radiation Sources) sectors 13 and 15, Advanced Photon Source at Argonne National Laboratory, with the support of the National Science Foundation, the U.S. Department of Energy and the W. M. Keck Foundation. The EMP analyses were supported by a grant to the California Institute of Technology from the Northern California Mineralogical Association. This study was funded, in part, by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County.
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Natural History Museum of Los Angeles County John Jago Trelawney EndowmentUNSPECIFIED
Northern California Mineralogical AssociationUNSPECIFIED
Subject Keywords:bobmeyerite; cerchiaraite; ashburtonite; new mineral; crystal structure; IR spectroscopy; electron microprobe analysis; cyclosilicate; Pb2+ 6s2 lone-electron pair; Mammot-Saint Anthony mine; Tiger, Arizona
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Record Number:CaltechAUTHORS:20130528-105407038
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ID Code:38687
Deposited On:30 May 2013 16:41
Last Modified:09 Nov 2021 23:39

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