MILOTAITE, PdSbSe, A NEW PALLADIUM MINERAL SPECIES FROM PˇREDBOˇRICE, CZECH REPUBLIC

Milotaite, chemically PdSbSe, is a new palladium mineral species discovered in a low-temperature selenium-rich assemblage at Předbořice, Czech Republic. It was observed in only one polished section, where it occurs as rare subhedral grains not exceed-ing 25 m in size. It is embedded in eucairite and tiemannite, and randomly intergrown with bornite and digenite. The other associated phases are chrisstanleyite, fischesserite, native gold, silver-rich hakite, tyrrellite, clausthalite, chaméanite and uraninite. The gangue is calcite. The synthetic equivalent of PdSbSe is megascopically silvery grey in color, has a metallic luster and a grey streak. It is brittle with an uneven fracture; no cleavage or parting can be observed. Values of VHN100 (12 indentations on three grains of synthetic PdSbSe) range between 420 and 514, mean 465 kg/mm2, which corresponds to a Mohs hardness of approxi-mately 4. In plane-polarized light, milotaite is white, isotropic and opaque, and lacks internal reflections. Reflectance data of both milotaite and its synthetic equivalent are provided. The average result of five electron-microprobe analyses of milotaite (two grains) is Pd 34.17, Cu 0.78, Ag 0.35, Sb 38.03, Se 26.38, total 99.71 wt.%, corresponding to Pd0.98Cu0.04Ag0.01Sb0.95Se1.02; synthetic PdSbSe (17 analyses on 4 grains) gave Pd 34.46, Sb 38.86, Se 26.60, total 99.91 wt.%, corresponding to Pd0.99Sb0.97Se1.04 (total atoms = 3). The synthetic PdSbSe has a cubic structure with a 6.3181(5) Å, V 252.20 (5) Å3, space group P213, and Z = 4. The calculated density is 8.09 g/cm3. The crystal structure was solved using synthetic PdSbSe. The strongest eight lines in the calculated powder-diffraction pattern derived from the results of the crystal-structure refinement [d in Å(I)(hkl)] are