Auerbakhite, MnTl 2 As 2 S 5 , a new thallium sulfosalt from the Vorontsovskoe gold deposit, Northern Urals, Russia

[摘要] Auerbakhite (IMA 2020–047), MnTl2As2S5, is a new sulfosalt from the Vorontsovskoe gold deposit, Sverdlovsk Oblast’, Northern Urals, Russia. The new mineral occurs in limestone breccias composed of calcite, dolomite, baryte,clinochlore, fluorapatite and quartz, and cemented by major realgar, orpiment and pyrite. Other minerals directly associating with auerbakhite include alabandite, bernardite, christite, cinnabar, coloradoite, dalnegroite, gillulyite, gold,hutchinsonite, imhofite, lorándite, metacinnabar, philrothite, rebulite, routhierite, sphalerite, and vrbaite. Auerbakhiteforms rare and very small short-prismatic crystals and irregular grains which do not exceed 15×5 µm. It is transparent,has a bright red color and adamantine luster. Auerbakhite is brittle, with an uneven fracture. Cleavage is not observed.The calculated density is 5.245 g/cm3. In reflected light, auerbakhite is light gray, weakly bireflectant. In crossed polars,it is distinctly anisotropic, in light gray and brown tones, with abundant bright red internal reflections. The empiricalformula of auerbakhite is Mn1.04Tl1.97Pb0.02As1.95S5.02 (based on 10 atoms pfu). Prominent features in the Raman spectruminclude bands of Mn–S and As–S stretching vibrations and numerous low-frequency bands related to mixed soft modesinvolving bending and Tl–S stretching vibrations. Auerbakhite is orthorhombic, space group Cmce, a = 15.3280(15)Å, b = 7.662(7)Å, c = 16.6330(14)Å, V = 1953.40(18)Å3 and Z = 8. The crystal structure of auerbakhite was refinedfrom the single-crystal X-ray diffraction data to R = 0.0723 for 307 observed reflections with Iobs > 3σ(I). Auerbakhiteis isostructural to the synthetic phase Tl2MnAs2S5. Its crystal structure consists of complex (001) layers based on a setof MnS4 columns parallel to [010] and are composed of edge-sharing slightly irregular MnS6 octahedra. The columnsare connected via Tl1 and are framed by paired AsS3 pyramids with lone electron pairs oriented into interlayer space.Highly irregular Tl(2)S6 coordination polyhedra are situated in interlayers and share ligands with the layers. The newmineral honors Russian mining engineer, manufacturer and mineralogist Alexander Andreevitch Auerbakh whose activities were closely related to Northern Urals.

[学科分类] 自动化工程

[关键词] auerbakhite;new sulfosalt;thallium;crystal structure;Vorontsovskoe gold deposit;Northern Urals