Argentotetrahedrite-(Zn), Ag-6(Cu4Zn2)Sb4S13, a new member of the tetrahedrite group

Argentotetrahedrite-(Zn), Ag-6(Cu4Zn2)Sb4S13, has been approved as a new mineral species by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA-CNMNC) using samples from Kremnica, Slovak Republic (hereafter KR), and Lengenbach, Switzerland (LE). Additionally, it was also identified at the small deposit of Zvestov (Stfibrnice), Czech Republic (ZV). At the Slovak locality, it occurs as anhedral grains up to 0.1 mm in size, steel-grey in colour, with a metallic lustre, in association with 'argentotennantite-(Fe)' and tiny chalcopyrite grains in quartz gangue. At Lengenbach, it was found as domains of tristetrahedral crystal of tetrahedrite-(Zn), up to 1 mm in size, associated with dolomite. At Zvestov, it occurs as irregular aggregates, up to 0.2 mm in size, partly rimmed by kenoargentotetrahedrite-(Fe). Argentotetrahedrite-(Zn) is isotropic, grey in colour, with blue-greenish tints. Reflectance data for COM wavelengths in air (KR sample) are [lambda (nm), R (%)]: 470, 30.1; 546, 29.8; 589, 29.8; and 650, 28.3. Chemical formulae of the samples studied, recalculated, on the basis of Sigma Me = 16 apfu (atoms per formula unit), are: (Ag3.27Cu2.69)Es-96[Cu-4.00(Zn1.69Fe0.23Cu0.05Cd0.02Hg0.01)Sigma(2.00)](Sb3.86As0.17)(Sigma 4.03)S-12.73 (KR), (Ag3.17Cu2.79)(Sigma 5.96)]Cu-4.00(Zn1.55Cd0.23Fe0.16Cu0.05Hg0.01)(Sigma 2.00)](Sb(3.71)AS(0.32))(Sigma 4.03)S-12.77 (LE) and (Ag3.27Cu2.67)(Sigma 5.94)[Cu-0.04(Zn1.39Fe0.50Cu0.03Hg0.00](Sigma 2.00)](Sb4.03As0.04)Sigma S-4.07(13.05 )(ZV). Argentotetrahedrite-(Zn) is cubic, 1 (4) over bar 3m, with a = 10.5505(10) angstrom, V = 1174.4(3) angstrom(3) and Z = 2 (KR); a = 105155(13) angstrom and V= 1162.8(4) angstrom(3) (LE); and a= 10.5663(12) angstrom and V= 1179.7 angstrom(3) (ZV). The crystal structure of argentotetrahedrite-(Zn) has been refined by single-crystal X-ray diffraction data to a final R-1 = 0.035 on the basis of 327 unique reflections with F-o > 4 sigma(F-o) and 22 refined parameters (sample KR). Argentotetrahedrite-(Zn) is isotypic with other members of the tetrahedrite group. The structural relationship between argentotetrahedrite-(Zn) and other members of the freibergite series are discussed and previous findings of this species are briefly reviewed.