GRAESERITE, Featisasol3(OH), a NEW MINERAL SPECIES of the DERBYLITE GROUP from the MONTE LEONE NAPPE, BINNTAL REGION, WESTERN AL
1083 The Canadian Mineralogist Vol.36, pp. 1083-1088(1998) GRAESERITE,FeaTisAsOl3(OH), A NEWMINERAL SPECIES OF THE DERBYLITE GROUP FROM THE MONTELEONE NAPPE, BINNTAL REGION, WESTERN ALPS, SWITZERLAND MICHAEL S. KRZEMNICKII Mineralagisch-Petrographischzs Instint, Universitiit Ba$eI, Bemoullistr. 30, CH-4056 Basel, Switzerl.and ERIC REUSSERI Iwtitut fiir Mincralogie und Petrographie, ETH-7zntram, Sonneggstr. 5, CH-8092 Zurich SwitzerLanl AssrRAcr Graeserite, ideally Fe4t3AsOl3(OH), is a new mineral species of the derbylite gloup, which includes derbylite, tomichite, a"ndhemloite. It is found in needle-shapedcrystals, elongate along the c axis. Graeserils i5 6sn6alinig, spacegtoup AXm, with the cell paramelersa 7 .184(2), b 14.289(6),c 5.006(2) A, p 105.17(2)",V 495.9(2) At, z=2, D,a.. =!.56 g/cm3.The VHNxgis_52L (Mohs hardness -595). The strongest five lines of the X-ray powder-diffraction pattern [d in An)(hkD] are: 2.681(100)@31), 2.846(80X131), 1.583(50X351), 3.117 (30)(220), nd 2.029(30)(122). Graeserite is black and metallic, with a black streak; it displays a conchoidal fracture. Pleochroism, bireflectance a"ndinternal reflections were not observed. The measured values of reflecrance in air are compared with those of other members of the derbylite group. Electron-microprobe analyses gave TiO2 40.89, Fe2O333.64, FeO"6" 3.94, PbO 5.00, As2O3 13.51,Sb2O3 1.43, and H2O"a" 1.30, loral 99.80 wt.7o. The empirical formula, based on 13 atoms of oxygen and one hydroxyl group, is (Fe3*z.qrFe2*o.gsTlos+Pbo.rs)>r.grTi3(As3*s.9aSb3*e.m)>r.orOrg(OH).
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