Steinmetzite, Zn2Fe3+(PO4)(2)(OH)center dot 3H(2)O, a new mineral formed from alteration of phosphophyllite at the Hagendorf Sud pegmatite, Bavaria

摘要

Steinmetzite, ideally Zn2Fe3+(PO4)(2)(OH)center dot 3H(2)O, is a new mineral from the Hagendorf-Stid pegmatite, Flagendorf, Oberpfalz, Bavaria, Gennany. Steinmetzite was found in a highly oxidized zone of the Cornelia mine at Hagendorf-Stid. It has formed by alteration of phosphophyllite, involving oxidation of the iron and some replacement of Zn by Fe. Steinmetzite lamellae co-exist with an amorphous Fe-rich phosphate in pseudomorphed phosphophyllite crystals. The lamellae are only a few um thick and with maximum dimension similar to 50 mu m. The phosphophyllite pseudomorphs have a milky opaque appearance, often with a glazed yellow to orange weathering rind and with lengths ranging from sub-mm to 1 cm. Associated minerals are albite, apatite, chalcophanite, jahnsite, mitridatite, muscovite, quartz and wilhelmgrimbelite. Goethite and cryptomelane are also abundant in the oxidized zone. The calculated density is 2.96 g cm(-3). Steinmetzite is biaxial (-) with measured refractive indices alpha = 1.642(2), beta = 1.659 (cal c.), gamma = 1.660(2) (white light). 2V(meas) = 27(1)degrees; orientation is Y approximate to b, X <^>c approximate to 27 degrees, with crystals flattened on {010} and elongated on [001]. Pleochroism shows shades of pale brown; Y > X approximate to Z. Electron microprobe analyses (average of seven crystals) with Fe reported as Fe2O3 and with H2O calculated from the structure gave ZnO 31.1, MnO 1.7, CaO 0.5, Fe2O3 21.9, Al2O3 0.3, P(2)o(5) 32.9, H2O 14.1 wt.%, total 102.5%. The empirical formula based on 2 P and 12 0, with all iron as ferric and OH adjusted for charge balance is Zn1.65Fe1.193+Mn0.112+ Ca0.03Al0.023+(PO4)(2)(OH)(1.21)center dot 2.79H(2)O. The simplified formula is Zn2Fe3+(PO4)(2)(OH)center dot 3H(2)O. Steinmetzite is triclinic, PI, with unit-cell parameters: a = 10.438(2), b= 5.102(1), c = 10.546(2) angstrom, alpha = 91.37(2), beta = 115.93(2) and gamma = 94.20(2)degrees. V= 502.7(3) angstrom(3), Z=2. The strangest lines in the powder X-ray diffraction pattern are [d(obs) in angstrom (I) (hkl)] 9.313(65) (100), 5.077(38) (010), 4.726(47) (002), 4.657(100) (200), 3.365 (55) ((3) over bar 02), 3.071(54) (1 (1) over bar2) and 2.735(48) ((3) over bar(1) over bar2). The structure is related to that of phosphophyllite.