Norilskite, (Pd,Ag)(7)Pb-4, a new mineral from Noril'sk-Talnakh deposit, Russia

摘要

Norilskite, (Pd,Ag)(7)Pb-4 is a new platinum-group mineral discovered in the Mayak mine of the Talnakh deposit, Russia. It forms anhedral grains in aggregates (up to similar to 400 mu m) with polarite, zvyagintsevite, Pd-rich tetra-auricupride, Pd-Pt bearing auricupride, Ag-Au alloys, (Pb,As,Sb) bearing atokite, mayakite, Bi-Pb-rich kotulskite and sperrylite in pentlandite, cubanite and talnakhite. Norilskite is brittle, has a metallic lustre and a grey streak. Values of VHN20 fall between 296 and 342 kg mm(2), with a mean value of 310 kg mm(2), corresponding to a Mohs hardness of similar to 4. In plane-polarized light, norilskite is orange-brownish pink, has moderate to strong bireflectance, orange-pink to greyish-pink pleochroism, and strong anisotropy; it exhibits no internal reflections. Reflectance values of norilskite in air (R-o, R-e' in %) are: 51.1, 48.8 at 470 nm, 56.8, 52.2 at 546 nm, 59.9, 53.5 at 589 nm and 64.7, 55.5 at 650 nm. Sixteen electron-microprobe analyses of natural norilskite gave an average composition: Pd 44.33, Ag 2.68, Bi 0.33 and Pb 52.34, total 99.68 wt.%, corresponding to the empirical formula (Pd6.56Ag0.39)(Sigma 6.95)(Pb3.97Bi0.03)(Sigma 4.00) based on 4 Pb + Bi atoms; the average of eight analyses on synthetic norilskite is: Pd 42.95, Ag 3.87 and Pb 53.51, total 100.33 wt.%, corresponding to (Pd6.25Ag0.56)(Sigma 6.81)Pb-4.00. The mineral is trigonal, space group P3(1)21, with a = 8.9656(4), c = 17.2801(8) angstrom, V = 1202.92(9) angstrom(3) and Z = 6. The crystal structure was solved and refined from the powder X-ray diffraction data of synthetic (Pd,Ag)(7)Pb-4. Norilskite crystallizes in the Ni13Ga3Ge6 structure type, related to nickeline. The strongest lines in the powder X-ray diffraction pattern of synthetic norilskite [d in angstrom (I) (hkl) ] are: 3.2201(29)(023,203), 2.3130(91)(026,206), 2.2414(100)(220), 1.6098(28)(046,406), 1.3076(38)(246,462), 1.2942(18)(600), 1.2115(37)(22.12,12.13), 0.9626(44)(06.12,60.12). The mineral is named for the locality, the Noril'sk district in Russia.