Argentopolybasite, Ag16Sb2S11, a new member of the polybasite group

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt


  • Martin Števko
  • Tomáš Mikuš
  • Jiří Sejkora
  • Jakub Plášil
  • Makovicky, Emil
  • Jozef Vlasáč
  • Anatoly Kasatkin

The new mineral argentopolybasite, ideally Ag16Sb2S11, was found at the Kremnica Au-Ag epithermal deposit, Ziar nad Hronom Co., Banská Bystrica Region, Slovakia (type locality), Sibenicny vrch near Nová Bana, Zarnovica Co., Banská Bystrica Region, Slovakia (cotype locality) and the Arykevaam epithermal Au-Ag deposit, Anadyr' District, Chukotka Autonomous Okrug, Russian Federation (cotype locality). At the Kremnica deposit argentopolybasite was found as discrete, well-developed (pseudo)hexagonal tabular crystals up to 4 mm in size or as complex crystalline aggregates and groups up to 5 mm in size in cavities of quartz. It is associated with pyrargyrite, polybasite, stephanite, miargyrite, rozhdestvenskayaite-(Zn), argentotetrahedrite-(Zn), naumannite, gold and pyrite. Argentopolybasite is dark grey to black, with a black streak and metallic to opaque lustre. The Mohs hardness is about 3. It is brittle without any observable cleavage and with a conchoidal fracture. The calculated density is 6.403 g cm-3. In reflected light, argentopolybasite is grey, without any observable bireflectance and very weak pleochroism. It shows moderate anisotropy in crossed polarisers with weak greenish and green-blue tints. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the IMA are (Rmin/Rmax, %): 30.3/31.0 (470 nm), 28.8/29.3 (546 nm), 28.1/28.6 (589 nm), 27.4/27.8 (650 nm). The empirical formulae (based on 29 apfu) are, Kremnica: (Ag15.94Cu0.18)16.12(Sb1.40As0.61)2.01(S10.60Se0.25Cl0.03)10.88, Nová Bana: Ag16.30(Sb1.74As0.22)1.96(S10.69Cl0.04)10.73 and Arykevaam: (Ag15.54Cu0.38)15.92(Sb1.56As0.51)2.07S11.01. The ideal end-member formula for argentopolybasite is Ag16Sb2S11. Argentopolybasite is trigonal, space group P321, a = 15.0646(5) A, c = 12.2552(5) A, V = 2408.61(15) A3 and Z = 2. The seven strongest X-ray powder diffraction lines are [dobs in A, (I), hkl]: 12.169, (40), 001; 3.162, (100), 041; 3.045, (54), 004; 2.881, (45), 042; 2.4256, (28), 421. The crystal structure of argentopolybasite from Kremnica, refined to Robs = 0.0741 for 2804 observed reflections, confirmed that the atomic arrangement is isotypic to that of the other members of the polybasite group and it is isostructural with argentopearceite.

TidsskriftMineralogical Magazine
Udgave nummer3
Sider (fra-til)382–395
StatusUdgivet - 2023

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