IMA 2018-075 = nipalarsite

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Marco E. Ciriotti
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IMA 2018-075 = nipalarsite

Messaggio da Marco E. Ciriotti » mar 05 nov, 2019 12:29

Prossima pubblicazione.

▪ Grokhovskaya, T.L., Karimova, O.V., Vymazalová, A., Laufek, F., Chareev, D., Kovalchuk, E.V., Magazina, L.O., Rassulov, V.A. (2019): Nipalarsite, Ni8Pd3As4, a new platinum-group mineral from the Monchetundra Intrusion, Kola Peninsula, Russia. Mineralogical Magazine, 83, (in press).

Nipalarsite, Ni8Pd3As4, is a new platinum-group mineral (PGM) discovered in the sulfide-bearing orthopyroxenite of the Monchetundra layered intrusion, Kola Peninsula, Russia (67°52'22", 32°47'60"). Nipalarsite forms anhedral grains (5-80 μm in size) in intergrowths with sperrylite, kotulskite, hollingworthite, isomertieite, menshikovite, palarstanide, nielsenite and monchetundtraite enclosed in pentlandite, anthophillite, actinolite and chlorite. Nipalarsite is brittle, has a metallic lustre and a grey streak. In plane-polarized light, nipalarsite is light gray with a blue tinge. Reflectance values in air (in %) are: 50.64 at 589nm, 46.06 at 470nm. 54.12 at 650nm and 48.74 at 546nm. Values of VHN20 fall between 400.5 and 449.2 kg mm–2, with a mean value of 429.9 kg mm–2, corresponding to a Mohs hardness of ∼4. The average result of 27 electron microprobe WDS analyses of natural nipalarsite is (in wt.%): Ni 44.011, Pd 28.74, Fe0.32, Cu 0.85, Pt 0.01, Au 0.05, As 25.42, Sb 0.05, Te 0.39, total 99.85. The empirical formula (normalized to 15 apfu) is: (Ni8.10Fe0.06)Σ8.16 (Pd2.94Cu0.18)Σ3.12 (As3.68Te0.03)Σ3.71 or, ideally, Ni8Pd3As4. Nipalarsite is cubic, space group Fm-3m, with a 11.4428(9) Å, V 1498.3(4) Å3, Z = 8. The strongest lines in the X-ray powder-diffraction pattern of synthetic Ni8Pd3As4 [d in Å (I) hkl] are: 2.859(10), 2.623(6), 2.557(6), 2.334(11), 2.201(35), 2.021(100), 1.906(8), 1.429(7). The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic Ni8Pd3As4. Identity between natural and synthetic nipalarsite is illustrated by an electron backscattered diffraction (EBSD) study of natural nipalarsite. The density calculated on the basis of the empirical formula of nipalarsite is 9.60 g/cm3. The mineral name corresponds to the three main elements: Ni, Pd, and As.
Marco E. Ciriotti

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