Arsenoústalečite, Cu12(As2Te2)Se13, a new mineral, and crystal structures of arsenoústalečite and stibioústalečite

Arsenoústalečite is a new mineral discovered in a sample collected from the abandoned & Uacute;stale & ccaron; deposit near Hora & zcaron;& dcaron;ovice, SW Bohemia, Czech Republic. It occurs as rare anhedral grains, up to 40 mu m in size, in a calcite gangue, associated with stibio & uacute;stale & ccaron;ite, hakite-(Hg), berzelianite and uraninite. Arseno & uacute;stale & ccaron;ite is dark grey, with a metallic lustre. Mohs hardness is ca. 3 1/2 -4; calculated density is 5.730 g/cm(3). In reflected light, arseno & uacute;stale & ccaron;ite is pale grey with a yellowish shade; it is isotropic. Internal reflections were not observed. Reflectance values for the four COM wavelengths in air [R (%) lambda (nm)] are: 33.3 (470); 33.1 (546); 33.0 (589); and 32.9 (650). The empirical formula of arseno & uacute;stale & ccaron;ite is (Cu5.81Ag0.17)(Sigma 5.98)(Cu5.95Fe0.02Zn0.02Hg0.01)(Sigma 6.00)(As1.40Sb0.87Te1.73)(Sigma 4.00)(Se10.30S2.32)Sigma(12.61). The ideal formula is Cu-12(As2Te2)Se-13, which requires (in wt.%) Cu (34.76), As (6.83), Te- 11.63, Se (46.78), total 100.00. Arseno & uacute;stale & ccaron;ite is cubic, I3m, with unit-cell parameters a = 10.6580(19) & Aring;, V = 1210.7(6) & Aring;(3) and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern [d, & Aring; (I, %) hkl] are: 3.077 (100) 222, 2.848 (10) 321, 1.946 (12) 521, 1.884(52) 440 and 1.608(21) 622. According to the single-crystal X-ray diffraction data (R1 = 0.0285 on the basis of 334 unique reflections with Fo > 4 sigma Fo and 24 refined parameters), arseno & uacute;stale & ccaron;ite is isotypic with other tetrahedrite-group minerals. The crystal structure of co-existing stibio & uacute;stale & ccaron;ite, with an empirical formula of (Cu5.69Ag0.07)(Sigma 5.76)(Cu5.80Zn0.13Fe0.06Hg0.01)(Sigma 6.00)(Sb1.82As0.42Te1.76)(Sigma 4.00)(Se9.52S3.10)(Sigma 12.62) and unit-cell parameters a = 10.6975(16) & Aring;, V = 1224.2(5) & Aring;(3) and Z = 2, was refined to R-1 = 0.0191 on the basis of 267 unique reflections with Fo > 4 sigma F-o and 24 refined parameters. Structural relationships and crystal-chemistry of both members of the & uacute;stale & ccaron;ite series are discussed. Arseno & uacute;stale & ccaron;ite is named after its type locality, the & Uacute;stale & ccaron; deposit and its chemical composition. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2022-116)