IMA 2017-112 = mitrofanovite

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Marco E. Ciriotti
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IMA 2017-112 = mitrofanovite

Messaggio da Marco E. Ciriotti » mer 03 ott, 2018 11:25

Prossima pubblicazione.

▪ Subbotin, V.V., Vymazalová, A., Laufek, F., Savchenko, Y.E., Stanley, C.J., Gabov, D.A., Plášil, J. (2018): Mitrofanovite, Pt3Te4, a new mineral from the East Chuarvy deposit, Fedorovo-Pana intrusion, Kola Peninsula, Russia. Mineralogical Magazine, 82, (in press).

Mitrofanovite, Pt3Te4 is a new telluride discovered in low-sulphide disseminated ore in the East Chuarvy deposit, Fedorovo-Pana intrusion, Kola Peninsula, Russia. It forms anhedral grains (up to about 20×50 μm) commonly in intergrowths with moncheite in aggregates with lukkulaisvaaraite, kotulskite, vysotskite, braggite, keithconnite, rustenburgite and Pt-Fe alloys hosted by a chalcopyrite-pentlandite-pyrrhotite matrix. Associated silicates are: orthopyroxene, augite, olivine, amphiboles, plagioclase. Mitrofanovite is brittle; it has a metallic lustre and a grey streak. Mitrofanovite has a good cleavage, along [001]. In planepolarized 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 synthetic analogue of mitrofanovite in air (Ro, Re’ in %) are: 58.4, 54.6 at 470nm; 62.7, 58.0 at 546nm; 63.4, 59.1 at 589nm; 63.6, 59.5 at 650nm. 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 (Pt2.91Pd0.02)Σ2.93(Te4.02Bi0.05)Σ4.07 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/cm3.The mineral is trigonal, space group R3m, with a 3.9874 (1), c 35.361 (1) Å, V 486.91 (2) Å3 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 X-ray powder diffraction pattern of synthetic mitrofanovite [d in Å (I) (hkl)] are: 11.790(23)(003), 5.891(100)(006), 2.851(26)(107), 2.137(16)(1013), 2.039(18)(0114), 1.574(24)(0120), 1.3098(21)(0027). The structural identity of natural mitrofanovite with synthetic Pt3Te4 was confirmed by electron backscatter diffraction (EBSD) 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 (PGE) mineralization in the Fedorova-Pana complex.
Marco E. Ciriotti

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