IMA 2016-105 = vymazalováite

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Marco E. Ciriotti
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IMA 2016-105 = vymazalováite

Messaggio da Marco E. Ciriotti » mar 11 lug, 2017 12:03

Prossima pubblicazione.

▪ Sluzhenikin, S.F., Kozlov, V.V., Stanley, C.J., Lukashova, M.L., Dicks, K. (2017): Vymazalováite, Pd3Bi2S2, a new mineral from the Noril'sk -Talnakh deposit, Krasnoyarskiy region, Russia. Mineralogical Magazine, 81, (in press).

Vymazalovaite, Pd3Bi2S2 is a new platinum-group mineral discovered in the Komsomolsky mine of the Talnakh deposit, Noril'sk district, Russia. It forms small (from a few μm to 20-35 μm) inclusions or euhedral grains in intergrowths of polarite, sobolevskite, acanthite, and unnamed (Pd,Ag)5BiS2 in aggregates (up to about 200 μm) in galena, rarely in chalcopyrite. It occurs with telargpalite, cooperite, braggite, vysotskite, sopcheite, stibiopalladinite, sobolevskite, moncheite, kotulskite, malyshevite, insizwaite, Au-bearing silver and the newly described mineral kravtsovite (PdAg2S) in association with pyrite, chalcopyrite, and galena in vein-disseminated mineralization in skarn rocks. Synthetic vymazalováite is brittle; it has a metallic lustre and a grey streak. In plane-polarized reflected light, vymazalováite is creamy grey and appears slightly brownish against galena in the assemblage with chalcopyrite. It exhibits no internal reflections. Average reflectance values in air for natural and synthetic vymazalováite are (R natural, R synthetic in %) are: 46.35, 45.7 at 470nm, 47.65, 47.45 at 546nm, 48.5, 48.2 at 589nm and 49.5, 49.0 at 650nm. Seven electron-microprobe analyses of vymazalováite give an average composition: Pd 40.42, Bi 49.15, Ag 0.55, Pb 1.02, S 7.77, and Se 0.26, total 99.17 wt.%, corresponding to the empirical formula Pd3.05(Bi1.89Ag0.04Pb0.04)Σ1.97(S1.95Se0.03)Σ1.98 based on a total of 7 atoms per formula unit. The simplified formula is Pd3Bi2S2. The mineral is cubic, space group I213, with a 8.3097(9) Å, V 573.79(1) Å3 and Z = 4. The density calculated on the basis of the empirical formula and cell dimensions of synthetic vymazalováite is 9.25 g/cm3 The strongest lines in the X-ray powder diffraction pattern of synthetic vymazalováite [d in Å (I) (hkl)] are: 4.15(32)(200), 2.93(78)(220), 2.40(100)(220), 2.08(53)(400), 1.695(34)(422), 1.468(35)(440), 1.252(31)(622). The structural identity of natural vymazalováite with synthetic Pd3Bi2S2 was confirmed by electron backscatter diffraction (EBSD) measurements on the natural sample. This new mineral honours Dr Anna Vymazalová of the Czech Geological Survey, Prague.
Marco E. Ciriotti

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