Kravtsovite, PdAg (sub 2) S, a new mineral from the Noril'sk-Talnakh Deposit, Krasnoyarskiy Kray, Russia

Kravtsovite, PdAg (sub 2) S, is a new platinum-group mineral discovered in the Komsomolsky mine of the Talnakh deposit, Noril'sk district, Russia. It forms equant inclusions (ranging in size from a few D:\Palash\HWNLM\07_06m to 40-50 D:\Palash\HWNLM\07_06m) in silicates and pyrite, commonly intergrown with vysotskite and Au-Ag alloy in aggregates (100-200 D:\Palash\HWNLM\07_06m across) with telargpalite, cooperite, braggite, vysotskite, sopcheite, stibiopalladinite, sobolevskite, moncheite, kotulskite, malyshevite and insizwaite. Kravtsovite is brittle; it has a metallic lustre and a grey streak. In plane-polarised light, kravtsovite is yellowish white, has strong bireflectance, is strongly pleochroic in shades of slightly yellowish white to bluish grey, and exhibits a strong anisotropy with rotation tints of salmon-pink, orange, pale blue and dark blue-black. It exhibits no internal reflections. Reflectance values in air (R (sub 1) , R (sub 2) in %) are: 32.2, 38.3 at 470, 31.6, 39.4 at 546, 30.2, 39.8 at 589 and 28.8, 41.1 at 650 nm. Eighteen electron probe microanalyses of kravtsovite give the average composition: Pd 30.53, Ag 60.11, S 8.47, and Se 0.74, total 99.85 wt%, corresponding to the empirical formula Pd (sub 1.03) Ag (sub 1.99) (S (sub 0.95) Se (sub 0.03) ) (sub Sigma 0.98) based on a total of 4 atoms per formula unit (apfu). The average of eight analyses on synthetic kravtsovite is: Pd 30.98, Ag 60.27, and S 8.81, total 100.07 wt%, corresponding to Pd (sub 1.04) Ag (sub 1.99) S (sub 0.98) . The mineral is orthorhombic, space group Cmcm, with a 7.9835(1), b 5.9265(1), c 5.7451(1) A, V 271.82(1) A (super 3) and Z = 4. The crystal structure was refined from the powder X-ray-diffraction data of the synthetic analogue. The strongest lines in the X-ray powder diffraction pattern of synthetic kravtsovite [d in A(I) (hkl)] are: 2.632(51)(021), 2.458(65)(112), 2.4263(71)(310), 2.3305(60)(202), 2.2352(100)(311), 2.1973(48) (221), 2.0619(42)(022), 1.9172(30)(130), 1.3888(31)(240,332), 1.3586(28)(512). The mineral honours V.F. Kravtsov, one of the discoverers of the Talnakh and Oktyabrsk deposits in the Noril'sk district of Russia.