Telluronevskite, Bi3TeSe2, a new mineral

Abstract

The new mineral telluronevskite, ideally Bi 3 TeSe 2 , has been found as irregular grains disseminated in quartzite from the volcanic Vihorlat Mts near Kosice in eastern Slovakia, Slovak Republic. The mineral forms massive aggregates up to 2 mm in diameter and/or individual disseminated tabular crystals flattened along (0001). Telluronevskite is megascopically steel grey in colour, with a metallic lustre and black streak. In reflected light, it is white with a yellow tint, very weak pleochroism and moderate anisotropy. Maximum and minimum values of reflectance measured in air for 470, 546, 589 and 650 nm are ( R max / R min in %): 48.5/46.6; 51.1/48.5; 51.9/49.5; 52.8/50.5. Vickers micro-hardness (VHN 10 in kp.mm −2 ) varied in the range 63-137 with mean value of 100. Microprobe analyses yield the empirical formula (Bi 2.92 Pb 0.02 )Te 1.01 (Se 1.73 S 0.32 ). It is trigonal with space group P 3 m 1. The unit-cell dimensions refined from X-ray powder microdiffraction data are a = 4.264(6) A and c = 23.25(3) A with c : a = 5.453 : 1. For Z = 2 the calculated density is D x = 8.08(2) g.cm −3 ; measured density D m = 8.1(2) g.cm −3 . The five strongest lines in the diffraction pattern are ( d (A), I/I 0 , hkl ): 4.66, 19, 005; 3.12, 100, 104; 2.28, 33, 108; 2.13, 36, 110, 109; 1.355, 18, 1.0.16, 214. Constrained structure refinement from combined powder and precession data revealed ordering of Te and Se atoms within the telluronevskite crystal structure. Telluronevskite belongs to the tsumoite subgroup of the tetradymite group.