Zavyalovite, Ag₂TeS₃, a new sulfotelluride from the Boevskoe deposit, Southern Urals, Russia

The new mineral zavyalovite, ideally Ag 2 TeS 3 , was found at the Boevskoe W-Be deposit, Chelyabinsk Oblast, Southern Urals, Russia.It occurs as very small anhedral grains (typically 5-15 m, max. up to 30 m across) or narrow veinlets (up to 100 5 m) within galena or at the contact of galena and sphalerite.Zavyalovite is dark red, opaque with sub-metallic luster, brittle tenacity and uneven fracture.No cleavage and parting are observed.The Vickers' micro-indentation hardness (VHN, 10 g load) is 95 kg/mm 2 (range 93-98, n = 4), corresponding to a Mohs' hardness of 2.5.D calc.= 5.33 g/cm 3 .In reflected light of the ore microscope, zavyalovite is grey, very weakly bireflectant and non-pleochroic.In crossed polarizers the new mineral exhibits strong anisotropy, in grey tones.Internal reflections are abundant, red in colour.The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (R min /R max , %): 32.2/31.8(470 nm), 29.6/29.1 (546 nm), 28.4/27.5 (589 nm) and 27.3/26.5(650 nm).The Raman spectrum shows bands corresponding to stretching and deformation vibrations in the TeS 3 polyhedra.The chemical composition (wt.%, electron microprobe data, mean of 8 spot analyses) is Ag 49.31, Te 29.04, S 21.75, total 100.10.The empirical formula calculated on the basis of 6 atoms per formula unit is Ag 2.01 Te 1.