РЕНИИТ, RESI - ПРИРОДНЫЙ ДИСУЛЬФИД РЕНИЯ ИЗ ФУМАРОЛ ВУЛКАНА КУДРЯВЫЙ (О. ИТУРУП, КУРИЛЬСКИЕ ОСТРОВА)

Abstract

Rheniite, RcS2, a natural rhenium disulfide, has been found among products of high temperature fumaroles of Kudriavy volcano, Iturup Island, Russia. It occurs as thin filmy (0.5-5 um) pseudohexagonal, rhombous and least often band-shaped curved plates up to 1.5-2 mm in size. There are both individual crystals and aggregates of such crystals in fissures of fumaroles crust. Aggregates cover someplace surfaces up to 10 X 10 cm and fill up cracks up to 3-S mm in width. Associated minerals are wollastonite, garnet of andradite-grossularite series, augite, magnetite, and sulfides: wurtzitc, cadmoindite, pyrite, and some other sublimated minerals. Rheniite crystallizes from the high temperature (450-600 °C) volcanic vapors by sublimation at depth between 20 and 60 cm. Mineral has silvery-white colour, grey-black streak and metallic luster. Under reflected light rheniite is white with slight pink hue. Bireflectance is grey to pinkish grey. Anisotropy is rather strong. Mineral is translucent and has red internal reflections. Individual flakes are elastic and/or brittle. Rheniite has perfect cleavage {001} and parting with pseudohexagonal symmetry. The microhardness cannot be determined because of tiny thickness. Calculated density is 7.S98 g/cm. Chemical composition, defined by 45 electron microprobc analyses [Camebax SX-50 and Camebax Micro-beam, Cameca (WDS)], shows Re 74.30 (73.28-75.90), Mo 0.13 (0.00-0.70), S 25.46 (23.69-26.04); the sum 99.89 (99.51-100.46) wt %. Its empirical formula, calculated on 3 atoms is Rei.oo2Moo.oosSi.993. Idealized formula is RcS2. The unit-cell parameters of rheniite were determined by the least squares from Guinicr data on sample mixed with Si powder as an internal standard. The observed data correspond basically to those of synthetic RcS2 (ASTM N 24-922). The strongest fifteen lines of X-ray powder diffraction pattern [d in A(/) (AW)] »e: 6.08 (7) (001); 2.7834 (10) (2 0 0); 2.764 (10) (0 2 T); 2.733 (10) (220); 2.642(8) (22 l]ij 2.404(8) (022); 2.371 (9) (201); 2.Г271 (7) (1 2T); 2.1035 (8) (320); 2X)914(9) (1 3 1); 1.8724 (9) (3 0 1); 1.8559 (8) (3 0 0); 1.6289 (9) (2 2 1); 1.6156 (10) (4 2 0); 1.5938 (10) (2 4 1). The unit cell parameters of rheniite are: a = 6.470 (5) A, 6 = 6.368(5) А, с = 6.401 (7) A, a =105.0(1)°, £= 91.59 (9)°, y= 118.90(6)°; K= 219.4(3) A3, Z = 4, Syngony is triclinic, space group P (1). Rheniite is na- med after its chemical composition as the unique mineral of rhenium. Type material is deposited in Fersman Mi-neralogical Museum RAS, Moscow.