SIDOROVITE, PtFe₃, A NEW MINERAL FROM THE SNEGOVAYA RIVER PLACER, KORYAK HIGHLANDS, RUSSIA

Sidorovite, ideally PtFe3, is a new mineral from the Epilchik ultramafic complex and nearby Snegovaya River placer, Koryak Highlands, Russia. It was found in isoferroplatinum grains extracted from a heavy-mineral concentrate obtained from crushed lode chromitites and alluvial material. Sidorovite occurs either as a part of complex grains comprising tetraferroplatinum, native iron, hollingworthite, magnetite, serpentine, and chromite or as part of secondary rims which formed together with tetraferroplatinum after isoferroplatinum. According to the Laue pattern obtained by synchrotron microdiffraction, sidorovite is cubic, crystallizing in space group Pm (3) over barm and adopting an Au3Cu-type crystal structure. Its unit-cell parameters are a = 3.725(4) angstrom, V = 51.687(4) angstrom(3), Z = 1. The calculated density is 11.815 g/cm(3). The strongest X-ray diffraction lines are [d (angstrom) (I, %) (hkl)] 2.161 (100) (111), 3.711 (48) (100), 1.871 (36) (200), 1.673 (27) (210). No cleavage was observed and hardness could not be determined owing to the small size of the grains. The empirical formula of sidorovite calculated based on four atoms is: Pt-1.04(Fe2.89Cu0.05Ni0.02)(Sigma 2.96). The mineral is posited to form through the incorporation of Fe-0 by tetraferroplatinum, which arises through the reduction of Fe via H-2-bearing fluids produced through the serpentinization of olivine at T < 450 degrees C. The name of the new mineral honors the Russian geologist and mineralogist Evgeniy Gennadievich Sidorov (1955-2021).