TY - JOUR
T1 - Nordgauite, MnAl2(PO4)2(F,OH)2·5H2O, a new mineral from the Hagendorf-Süd pegmatite, Bavaria, Germany: description and crystal structure
AU - Birch, W
AU - Grey, Ian
AU - Mills, S J
AU - Pring, Allan
AU - Bougerol, Catherine
AU - Ribaldi-Tunnicliffe, A
AU - Wilson, N
AU - Keck, E
PY - 2011
Y1 - 2011
N2 - 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 μm long and 10 μm 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. D meas. and D calc. 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, Al2O3 22.84, P2O5 31.62, F 5.13 and H2O 22.86 (by CHN), less F=O 2.16, total 96.50. The corresponding empirical formula is (Mn0.90Ca0.08Fe 0.04Zn0.01Mg0.01) Σ1.04Al2.01(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)(110), 4.119 (20)(210), 2.951 (16)(03̄1), 4.596 (12)(21̄0), 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 R 1 = 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.
AB - 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 μm long and 10 μm 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. D meas. and D calc. 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, Al2O3 22.84, P2O5 31.62, F 5.13 and H2O 22.86 (by CHN), less F=O 2.16, total 96.50. The corresponding empirical formula is (Mn0.90Ca0.08Fe 0.04Zn0.01Mg0.01) Σ1.04Al2.01(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)(110), 4.119 (20)(210), 2.951 (16)(03̄1), 4.596 (12)(21̄0), 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 R 1 = 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.
KW - crystal structure
KW - Germany
KW - Hagendorf-Süd pegmatite
KW - new mineral
KW - nordgauite
KW - phosphate
UR - http://www.scopus.com/inward/record.url?scp=79959944283&partnerID=8YFLogxK
U2 - 10.1180/minmag.2011.075.2.269
DO - 10.1180/minmag.2011.075.2.269
M3 - Article
SN - 0026-461X
VL - 75
SP - 269
EP - 278
JO - Mineralogical Magazine
JF - Mineralogical Magazine
IS - 2
ER -