Tetrahedrite-(Cu), Cu12Sb4S13, from Bankov near Košice, Slovak Republic: a new member of the tetrahedrite group

Tetrahedrite-(Cu), Cu12Sb4S13, has been approved as a new mineral species (IMA2022-078) from the Bankov magnesite deposit near Ko & scaron;ice, Slovak Republic where it occurs as anhedral grains, up to 0.4 mm across, associated with skinnerite, chalcostibite, famatinite, tetrahedrite-(Fe) and zoned aggregates of tennantite-(Cu) to tennantite-(Fe). Tetrahedrite-(Cu) is steel-grey, with a metallic lustre. Mohs hardness is ca. 3 1/2 -4 and calculated density is 5.029 g.cm-3. In reflected light, tetrahedrite-(Cu) is isotropic and grey with a bluish shade. Reflectance data for the four COM wavelengths in air are [lambda (nm): R (%)]: 470: 31.1; 546: 30.1; 589: 29.9; and 650: 28.1. The empirical formula, based on electron-microprobe data (mean of 17 spot analyses), is Cu11.42Zn0.26Fe0.19(Sb4.06As0.08)Sigma 4.14S12.99. The ideal formula is Cu6(Cu4Cu2)Sb4S13, which requires (in wt.%) Cu 45.76, Sb 29.23 and S 25.01, total 100.00. Tetrahedrite-(Cu) is cubic, I3m, with unit-cell parameters a = 10.3296(15) & Aring;, V = 1102.2(5) & Aring;3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0347 on the basis of 261 unique reflections with Fo > 4 sigma(Fo) and 22 refined parameters. Tetrahedrite-(Cu) is isotypic with other tetrahedrite-group minerals. Previous findings of tetrahedrite-(Cu) are reported and some nomenclature issues, related to the Fe and Cu oxidation states, are discussed. At the Bankov deposit, tetrahedrite-(Cu) is related to hydrothermal, most probably Alpine, solutions strongly enriched in Cu, Sb and S.