Zincoberaunite, ZnFe53+(PO4)(4)(OH)(5)center dot 6H(2)O, a new mineral from the Hagendorf South pegmatite, Germany

摘要

The new mineral zincoberaunite, ideally ZnFe3+ (5)(PO4)(4)(OH)(5)center dot 6H(2)O, the Zn analogue of beraunite, is found in the Hagendorf South granitic pegmatite, Hagendorf, Bavaria, Germany, in two associations: (1) with potassium feldspar, quartz, jungite, phosphophyllite and mitridatite (the holotype) and (2) with flurlite, plimerite, Zn-bearing beraunite, schoonerite, parascholzite/scholzite, robertsite and altered phosphophyllite (the cotype). Zincoberaunite occurs as radial or randomly oriented aggregates of flexible fibers up to 1.5 mm long and up to 3 mu m thick. D (calc) is 2.92 g/cm(3) for the holotype and 2.94 g/cm(3) for the cotype. Zincoberaunite is optically biaxial (-), alpha = 1.745(5), beta = 1.760(5), gamma = 1.770(5), 2V (meas) = 80(5)A degrees. Chemical composition of the holotype (electron probe microanalyser; H2O by gas chromatography of ignition products) is: MgO 0.28 wt%, CaO 0.47 wt%, ZnO 7.36 wt%, Al2O3 0.88 wt%, Fe2O3 42.42 wt%, P2O5 31.63 wt%, H2O 16.2 wt%, total 101.1 wt%. The empirical formula calculated on the basis of 27 oxygen atoms per formula unit is (Zn0.83Ca0.08Mg0.06)(a0.97)(Fe3+ Al-4.88(0.16))(Sigma 5.04)(PO4)(4.09)(OH)(4.78) center dot 5.86H(2)O. Zincoberaunite is monoclinic, space group C2/c; refined unit cell parameters (for the holotype at room temperature and the cotype at 100 K, respectively) are: a 20.837(2) and 20.836(4), b 5.1624(4) and 5.148(1), c 19.250(1) and 19.228(4) , angstrom,beta 93.252(5) and 93.21(3)degrees, V 2067.3(3) and 2059.2(7) angstrom(3), Z = 4. The crystal structure of the holotype specimen has been refined by the Rietveld method (R (p) = 0.30 %; R (B) = 0.18 %) whereas the structure of the cotype has been solved from the single crystal data and refined to R (1) = 0.056 based on 1900 unique reflections with I > 2 sigma(I). The strongest reflections of the powder X-ray diffraction pattern of the holotype specimen [(d, ) (I, %) (hkl)] are: 10.37 (100) (200), 9.58 (32) (002), 7.24 (26) (20-2), 4.817 (22) (111), 4.409 (13) (112), 3.483 (14) (11-4, 600), 3.431 (14) (404), 3.194 (15) (006, 31-4), 3.079 (33) (314).