Mitrofanovite, Pt3Te4, a new mineral from the East Chuarvy deposit, Fedorovo-Pana intrusion, Kola Peninsula, Russia

Mitrofanovite, Pt3Te4, is a new telluride discovered in low-sulfide disseminated ore in the East Chuarvy deposit, Fedorovo-Pana intrusion, Kola Peninsula, Russia. It forms anhedral grains (up to similar to 20 mu m x 50 mu m) commonly in intergrowths with moncheite in aggregates with lukkulaisvaaraite, kotulskite, vysotskite, braggite, keithconnite, rustenburgite and Pt-Fe alloys hosted by a chalcopyrite-pentlanditepyrrhotite matrix. Associated silicates are: orthopyroxene, augite, olivine, amphiboles and plagioclase. Mitrofanovite is brittle; it has a metallic lustre and a grey streak. Mitrofanovite has a good cleavage, along {001}. In plane-polarised light, mitrofanovite is bright white with medium to strong bireflectance, slight pleochroism, and strong anisotropy on non-basal sections with greyish brown rotation tints; it exhibits no internal reflections. Reflectance values for the synthetic analogue of mitrofanovite in air (R-o, R-e, in %) are: 58.4, 54.6 at 470 nm; 62.7, 58.0 at 546 nm; 63.4, 59.1 at 589 nm; and 63.6, 59.5 at 650 nm. Fifteen electron-microprobe analyses of mitrofanovite gave an average composition: Pt 52.08, Pd 0.19, Te 47.08 and Bi 0.91, total 100.27 wt.%, corresponding to the formula (Pt-2.(91) Pd-0.02)(Sigma 2)(.)(93) (Te4.02Bi0.05)(Sigma 4)(.)(07) based on 7 atoms; the average of eleven analyses on synthetic analogue is: Pt 52.57 and Te 47.45, total 100.02 wt.%, corresponding to Pt2.94Te4.06. The density, calculated on the basis of the formula, is 11.18 g/cm(3). The mineral is trigonal, space group R (3) over barm, with a = 3.9874(1), c = 35.361(1) angstrom, V = 486.91(2) angstrom(3) and Z = 3. The crystal structure was solved and refined from the powder X-ray-diffraction data of synthetic Pt3Te4. Mitrofanovite is structurally and chemically related to moncheite (PtTe2). The strongest lines in the powder X-ray diffraction pattern of synthetic mitrofanovite [d in angstrom (I) (hkl)] are: 11.790(23)(003), 5.891 (100)(006), 2.851(26)(107), 2.137(16)(10 (13) under bar), 2.039(18)(01 (14) under bar), 1.574(24)(01 (20) under bar), 1.3098(21)(00 (27) under bar). The structural identity of natural mitrofanovite with synthetic Pt3Te4 was confirmed by electron backscatter diffraction measurements on the natural sample. The mineral name is chosen to honour Felix P. Mitrofanov, a Russian geologist who was among the first to discover platinum-group element mineralisation in the Fedorova-Pana complex.