Selenodantopaite, Ag ₅ Bi ₁₃ Se ₂₂ , a new member of the pavonite homologous series from Potůčky, Czech Republic

Abstract Selenodantopaite is a new mineral species discovered in a sample collected from the mine dumps of the abandoned Princ Evžen deposit near Potůčky, the Krušné hory Mts., Czech Republic. Selenodantopaite occurs as anhedral grains, up to 100 μm in size, in a quartz gangue with abundant coffinitized uraninite, chalcopyrite and pyrite; it is also associated with bohdanowiczite, unnamed selenide (Bi,Ag) 3 (Se,S,Te) 4 , minerals of the galena–clausthalite solid solution, sphalerite and tennantite-(Fe). Selenodantopaite is dark grey, with metallic lustre. Mohs hardness is ca . ∼3½, calculated density is 7.403 g.cm –3 . In reflected light, selenodantopaite is white to light grey; bireflectance and pleochroism are weak, anisotropy is distinct with light bluish white – light purplish brown rotation tints. Internal reflections were not observed. Reflectance values for the four COM wavelengths of selenodantopaite in air [ R max , R min (%) (λ in nm)] are: 48.3, 44.9 (470); 48.8, 45.3 (546); 48.4, 45.1 (589); and 47.7, 44.6 (650). The empirical formulae, based on electron-microprobe analyses, are Cu 0.24(4) Ag 5.09(7) Fe 0.17(5) Pb 0.51(4) Bi 12.32(21) Se 15.11(21) S 6.89(21) and Cu 0.05(3) Ag 5.23(11) Fe 0.06(4) Pb 0.62(12) Bi 12.38(13) Se 14.77(16) S 7.23(16) for Cu-bearing and Cu-poor variety, respectively. The ideal formula is Ag 5 Bi 13 Se 22 ( Z = 1), which requires (in wt.%) Ag 10.80, Bi 54.41, and Se 34.79, total 100.00. Selenodantopaite is monoclinic, C 2 /m , with unit-cell parameters a = 13.670(4), b = 4.1400(11), c = 19.282(6) Å, β = 106.385(11)° and V = 1046.9(5) Å 3 . According to the single-crystal X-ray diffraction data ( R 1 = 0.0625), the crystal structure of selenodantopaite is isotypic with that of dantopaite and it is composed by two kinds of slabs, parallel to (001), i.e. a PbS-like thick slab and a thin slab, following the classical structural scheme of pavonite homologues. Selenodantopaite is named in accord with its composition and its relationship with dantopaite. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (2023-092)