IMA 2017-012 = schmidite / IMA 2017-058 = wildenauerite

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Marco E. Ciriotti
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IMA 2017-012 = schmidite / IMA 2017-058 = wildenauerite

Messaggio da Marco E. Ciriotti » lun 02 lug, 2018 10:14

Prossima pubblicazione.

▪ Grey, I.E., Keck, E., Kampf, A.R., Cashion, J.D., Macrae, C.M., Glenn, A.M., Gozukara, Y. (2018): Schmidite and wildenauerite, two new schoonerite-group minerals from the Hagendorf Süd pegmatite, Oberpfalz, Bavaria. Mineralogical Magazine, 82, (in press).

Schmidite, Zn(Fe3+0.5Mn2+0.5)2ZnFe3+(PO4)3(OH)3(H2O)8 and wildenauerite, Zn(Fe3+0.5Mn2+0.5)2Mn2+Fe3+(PO4)3(OH)3(H2O)8 are two new oxidized schoonerite-group minerals from the Hagendorf-Süd 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 α = 1.642(2), β = 1.680(1), γ = 1.735(2), 2V(meas) = 81.4(8)° for schmidite, and with α = 1.659(3), β = 1.687(3), γ = 1.742(3), 2V(meas) = 73(1) for wildenauerite. Electron microprobe analyses, with H2O from thermal analysis and FeO/Fe2O3 from Mössbauer spectroscopy, gave FeO 0.4, MgO 0.3, Fe2O3 23.5, MnO 9.0, ZnO 15.5, P2O5 27.6, H2O 23.3, total 99.6 wt% for schmidite, and FeO 0.7, MgO 0.3, Fe2O3 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 Zn1.47Mn2+0.98Mg0.05Fe2+0.04Fe3+2.27(PO4)3(OH)2.89(H2O)8.54 for schmidite and Zn1.11Mn2+1.18Mg0.05Fe2+0.08Fe3+2.47(PO4)3(OH)3.25(H2O)9.03 for wildenauerite. The two minerals have orthorhombic symmetry, Pmab, Z = 4. The unit-cell parameters from refinement of powder XRD data are a = 11.059(1), b = 25.452(1) and c = 6.427(1) Å for schmidite, and a = 11.082(1), b = 25.498(2) and c = 6.436(1) Å for wildenauerite. The crystal structures of schmidite and wildenauerite differ from that of schoonerite in having minor partitioning of Zn from the [5]Zn site to an adjacent vacant tetrahedral site [4]Zn, separated by ~1.0 Å from [5]Zn. The two minerals are distinguished by the cation occupancies in the octahedral M1 to M3 sites. Schmidite has M1 = M2 = (Fe3+0.5Mn2+0.5), M3 = Zn and wildenauerite has M1 = M2 = (Fe3+0.5Mn2+0.5), M3 = Mn2+.
Marco E. Ciriotti

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