Schmidite and wildenauerite, two new schoonerite-group minerals from the Hagendorf-Sud pegmatite, Oberpfalz, Bavaria

摘要

Schmidite, Zn(Fe0.53+M0.52+)(2)ZnFe3+(PO4)(3)(OH)(3)(H2O)(8) and wildenauerite, Zn(Fe0.53+M0.52+)(2)Mn2+Fe3+(PO4)(3)(OH)(3)(H2O)(8) are two new oxidised schoonerite-group minerals from the Hagendorf-Sfid pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany. Schmidite occurs as radiating sprays of orange-brown to copper-red laths on and near to altered phosphophyllite in a corroded triphylite nodule, whereas wildenauerite forms dense compacts of red laths, terminating Zn-bearing rockbridgeite. The minerals are biaxial (+) with alpha = 1.642(2), beta = 1.680(1), gamma = 1.735(2) and 2V(meas) = 81.4(8)degrees for schmidite, and with alpha = 1.659(3), beta = 1.687(3), gamma = 1.742(3) and 2V(meas) = 73(1)degrees for wildenauerite. Electron microprobe analyses, with H2O from thermal analysis and FeO/Fe2O3 from Mossbauer spectroscopy, gave FeO 0.4, MgO 0.3, Fe2O3 23.5, MnO 9.0, ZnO 15.5, P(2)O(5 )27.6, H2O 23.3, total 99.6 wt.% for schmidite, and FeO 0.7, MgO 0.3, Fe(2)O(3 )25.2, MnO 10.7, ZnO 11.5, P2O5 27.2, H2O 24.5, total 100.1 wt.% for wildenauerite. The empirical formulae, scaled to 3 P and with OH- adjusted for charge balance are Zn1.47Mn0.982+Mg0.05Fe0.042+Fe2.273+(PO4)(3)(OH)(2.89)(H2O)(8.54) for schmidite and Zn1.11Mn1.182+Mg0.05Fe0.082+Fe2.473+(PO4)(3)(OH)(3.25)(H2O)(9.03) for wilde-nauerite. The two minerals have orthorhombic symmetry, space group Pmab and Z = 4. The unit-cell parameters from refinement of powder X-ray diffraction data are a = 11.059(1), b = 25.452(1) and c= 6.427(1) angstrom for schmidite, and a = 11.082(1), b = 25.498(2) and c = 6.436 (1) angstrom for wildenauerite. The crystal structures of schmidite and wildenauerite differ from that of schoonerite in having minor partitioning of Zn from the Zn-[5] site to an adjacent vacant tetrahedral site Zn-[4], separated by similar to 1.0 angstrom from Zn-[5]. The two minerals are distinguished by the cation occupancies in the octahedral M1 to M3 sites. Schmidite has M1= M2 = (Fe0.53+Mn0.52+) and M3 = Zn and wildenauerite has M1= M2 = (Fe0.53+Mn0.52+) and M3 = Mn2+.