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For the first time, chromium disulphides, known from meteorites, such as caswellsilverite, NaCrS₂; grokhovskyite, CuCrS₂; and a potentially new mineral, AgCrS₂, as well as the products of their alteration, such as schöllhornite, Na_0.3CrS₂∙H₂O, and a potentially new mineral with the formula {Fe_0.3(Ba,Ca)_0.2} CrS₂·0.5H₂O, have been found in terrestrial rock. Layered chromium disulphides were found in unusual phosphide-bearing breccia of the pyrometamorphic Hatrurim Complex in the Negev Desert, Israel. The chromium disulphides belong to the central fragment of porous gehlenite paralava cementing altered host rock clasts. The empirical formula of caswellsilverite is (Na_0.77Sr_0.03Ca_0.01)_Σ0.81(Cr³⁺_0.79Cr⁴⁺_0.18V³⁺_0.01 Fe³⁺_0.01)_Σ0.99S₂·0.1H₂O, and the end-member content of NaCrS₂ is 76%. It forms single crystals in altered pyrrhotite aggregates. Grokhovskyite has the empirical formula {Cu⁺_0.84Fe³⁺_0.10Ca_0.06 Na_0.01 Sr_0.01Ba_0.01}_Σ1.03(Cr³⁺_0.94 Fe³⁺_0.05 V³⁺_0.05)_Σ1.00S₂·0.35H₂O, and the CuCrS₂ end-member content is 75–80%. A potentially new Ag-bearing chromium disulphide is characterised by the composition (Ag_0.89Cu_0.07)_Σ0.96(Cr_0.98 Fe_0.03V_0.01Ni_0.01)_Σ1.04S₂. Caswellsilverite, grokhovskyite and AgCrS₂ form in gehlenite paralava at high temperatures (near 1000 °C) and low pressure under reducing conditions. The structure of the layered chromium disulphides, MCrS₂, is characterised by the presence of hexagonal octahedral layers (CrS₂)¹⁻, between which M-sites of the monovalent cations Ag, Cu and Na set. A low-temperature alteration of the layered chromium disulphides, when schöllhornite and {Fe_0.3(Ba,Ca)_0.2}CrS₂·0.5H₂O form, is reflected in the composition and structural modification of the layer with monovalent cations, whereas the octahedral layer (CrS₂)¹⁻ remains unchanged. Full article

Uakitite was observed in small troilite–daubréelite (±schreibersite) inclusions (up to 100 µm) and in large troilite–daubréelite nodules (up to 1 cm) in Fe-Ni-metal (kamacite) of the Uakit iron meteorite (IIAB), Republic of Buryatia, Russia. Such associations in the Uakit meteorite seemed to form due to high-temperature (>1000 °C) separation of Fe-Cr-rich sulfide liquid from Fe-metal melt. Most inclusions represent alternation of layers of troilite and daubréelite, which may be a result of solid decay of an initial Fe-Cr-sulfide. These inclusions are partially resorbed and mainly located in fissures of the meteorite, which is now filled with magnetite, and rarely other secondary minerals. Phase relations indicate that uakitite is one of the early minerals in these associations. It forms isometric (cubic) crystals (in daubréelite) or rounded grains (in schreibersite). The size of uakitite grains is usually less than 5 μm. It is associated with sulfides (daubréelite, troilite, grokhovskyite), schreibersite and magnetite. Carlsbergite CrN, a more abundant nitride in the Uakit meteorite, was not found in any assemblages with uakitite. Physical and optical properties of uakitite are quite similar to synthetic VN: yellow and transparent phase with metallic luster; Mohs hardness: 9–10; light gray color with a pinky tint in reflected light; density (calc.) = 6.128 g/cm³. Uakitite is structurally related to the osbornite group minerals: carlsbergite CrN and osbornite TiN. Structural data were obtained for three uakitite crystals using the electron backscatter diffraction (EBSD) technique. Fitting of the EBSD patterns for a synthetic VN model (cubic, Fm-3m, a = 4.1328(3) Å; V = 70.588(9) ų; Z = 4) resulted in the parameter MAD = 0.14–0.37° (best-good fit). Analytical data for uakitite (n = 54, in wt. %) are: V, 71.33; Cr, 5.58; Fe, 1.56; N, 21.41; Ti, below detection limit (<0.005). The empirical formula (V_0.91Cr_0.07Fe_0.02)_1.00N_1.00 indicates that chromium incorporates in the structure according to the scheme V³⁺ → Cr³⁺ (up to 7 mol. % of the carlsbergite end-member). Full article