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Nordgauite, MnAl2(PO4)2(F,OH)2·5H2O, a new mineral from the Hagendorf-Süd pegmatite, Bavaria, Germany: description and crystal structure

Published online by Cambridge University Press:  05 July 2018

W. D. Birch ,
I. E. Grey ,
S. J. Mills ,
A. Pring ,
C. Bougerol ,
A. Ribaldi-Tunnicliffe ,
N. C. Wilson  and
E. Keck
W. D. Birch*
Affiliation:
Geosciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia
I. E. Grey
Affiliation:
CSIRO Process Science and Engineering, PO Box 312, Clayton, 3169, Victoria, Australia
S. J. Mills
Affiliation:
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
A. Pring
Affiliation:
Mineralogy Department, South Australian Museum, North Terrace, Adelaide, South Australia 5000
C. Bougerol
Affiliation:
CEA-CNRS-UJF group ‘Nanophysique et Semiconducteurs’, Institut Néel, CNRS-Université Joseph Fourier, 38042 Grenoble, France
A. Ribaldi-Tunnicliffe
Affiliation:
Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
N. C. Wilson
Affiliation:
CSIRO Process Science and Engineering, PO Box 312, Clayton, 3169, Victoria, Australia
E. Keck
Affiliation:
Algunderweg 3, 92694 Etzenricht, Germany
*
*E-mail: [email protected]
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Abstract

Nordgauite, MnAl2(PO4)2(F,OH)2·5H2O, is a new secondary phosphate from the Hagendorf-Süd pegmatite, Bavaria, Germany. It occurs as white to off-white compact waxy nodules and soft fibrous aggregates a few millimetres across in altered zwieselite—triplite. Individual crystals are tabular prismatic, up to 200 μ long and 10 μ wide. Associated minerals include fluorapatite, sphalerite, uraninite, a columbite—tantalite phase, metastrengite, several unnamed members of the whiteite—jahnsite family, and a new analogue of kingsmountite. The fine-grained nature of nordgauite meant that only limited physical and optical properties could be obtained; streak is white; fracture, cleavage and twinning cannot be discerned. Dmeas. and Dcaic. are 2.35 and 2.46 g cm–3, respectively; the average RI is n = 1.57; the Gladstone-Dale compatibility is —0.050 (good). Electron microprobe analysis gives (wt.%): CaO 0.96. MgO 0.12, MnO 14.29, FeO 0.60, ZnO 0.24, A12O3 22.84, P2O5 31.62, F 5.13 and H2O 22.86 (by CHNX less F=O 2.16, total 96.50. The corresponding empirical formula is (Mn0.90Ca0.08Fe0.04Zn0.01Mg0.01)-Σi.04Ai2.0i(PO4)2[F1.21,(OH)0.90]Σ2.11·5.25H2O. Nordgauite is triclinic, space group P1̄, with the unit-cell parameters: a = 9.920(4), b = 9.933(3), c = 6.087(2) Å, α = 92.19(3), β = 100.04(3), γ = 97.61(3)°, V = 584.2(9) Å3 and Z = 2. The strongest lines in the XRD powder pattern are [d in Å (I) (hkl)] 9.806 (100)(010), 7.432 (40)(l1̄0), 4.119 (20)(210), 2.951 (16)(031), 4.596 (12)(21̄O), 3.225 (12)(220) and 3.215 (12)(121). The structure of nordgauite was solved using synchrotron XRD data collected on a 60 μm × 3 μm × 4 μm needle and refined to R1 = 0.0427 for 2374 observed reflections with F > 4σ(F). Although nordgauite shows stoichiometric similarities to mangangordonite and kastningite, its structure is more closely related to those of vauxite and montgomeryite in containing zig-zag strings of corner-connected Al-centred octahedra along [011], where the shared corners are alternately in cis and trans configuration. These chains link through corner-sharing with PO4 tetrahedra along [001] to form (100) slabs that are interconnected via edge-shared dimers of MnO6 polyhedra and other PO4 tetrahedra.

Keywords

nordgauitenew mineralHagendorf-Süd pegmatiteGermanyphosphatecrystal structure
Type
Research Article
Information
Mineralogical Magazine , Volume 75 , Issue 2 , April 2011 , pp. 269 - 278
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2011

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Anisotropic displacement factors and Calculated structure factors

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