Cuprokalininite, CuCr2S4, a new sulfospinel from metamorphic rocks of the Sludyanka Complex, South Baikal region

Cuprokalininite as an accessory mineral has been found in Cr-V-bearing quartz-diopside metamorphic rock of the Sludyanka Complex, South Baikal region, Russia. This mineral is named as Cu analogue of kalininite (ZnCr₂S₄), is associated with quartz, Cr-V-bearing tremolite and mica, calcite, diopside-kosmochlor, goldmanite-uvarovite, dravite-chromdravite, Cr-V spinellide, karelianite-eskolaite, V-bearing titanite, pyrite, and plagioclase. Cuprokalininite forms euhedral microcrystals up to 0.05–0.20 mm in size, of octahedral and cuboctahedral habit with faces o {111} and a {100}, and polysynthetic and simple twinning along the {111}. Cleavage and parting were not observed. The mineral is black with a dark bronze tint, black streak, and metallic luster. The microhardness (VHN) is 356–458 (loadings are 20 and 30 g), 396 kgf/mm², on average. The Mohs hardness is 4.5–5.0, d _calc = 4.16(2). In reflected light, the mineral is pale-cream-colored, without anisotropy; reflectance values (λ, nm-R, %): 400-34.3, 420-34.1, 440-33.9, 460-33.7, 480-33.5, 500-33.2, 520-33.0, 540-32.8, 560-32.3, 580-32.2, 600-31.9, 620-31.6, 640-31.2, 660-30.9, 680-30.6, 700-30.4. Cubic, space group Fd `3]\bar 3 m, Z = 8; unit cell parameter a = 9.814(2) ?, V = 945.2(4) ?³. The strongest lines of the X-ray powder diffraction pattern d, ? (I) (hkl)]: 3.44 (6)(220), 2.94 (10)(311), 2.44 (6)(400), 1.884 (9)(511, 333), 1.731 (10)(440), 1.133 (6)(751, 555), 1.098 (6)(840), 1.030 (6)(931), 1.002 (10)(844). Chemical composition (mean of 202 microprobe analyses of 11 grains, wt %): Cu 21.03, Fe 0.47, Zn 0.17, Cr 29.01, V 5.85, As 0.21, Sb 0.08, S 43.25; the total is 100.07. The empirical formula calculated on the basis of seven ions is (Cu_0.98Fe_0.02Zn_0.01)_1.01(Cr_1.65V_0.34As_0.01)_2.00S_3.99. The type material has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.