Tillmannsite, (Ag3Hg)(V,As)O4, a new mineral: its description and crystal structure
Sarp, Halil; Pushcharovsky, Dmitry Y.u.; MacLean, Elizabeth J.; Teat, Simon J.; Zubkova, Natalia V.
European Journal of Mineralogy Volume 15 Number 1 (2003), p. 177 - 180
published: Feb 17, 2003
ArtNo. ESP147051501017, Price: 29.00 €
Tillmannsite, (Ag3Hg)(V,As)O4, was found in the old copper mines of Roua (Alpes-Maritimes, France), associated with pecoraite, vésigniéite, olivenite, kolfanite, janggunite, chlorargyrite, cuprite, native copper, native silver, native silver containing 2 % of mercury, domeykite, djurleite and algodonite. It forms aggregates (0.2 mm diameter) consisting of pseudooctahedral crystals (50μm maximum dimension). The crystals are red, brownish red. The mineral is tetragonal, I4, a = 7.727(7) Å, c = 4.648(5) Å, V = 277.5(5) Å3, Z = 2 and Dcalc = 7.733(3) g/cm3. The strongest lines in the X-ray powder diffraction pattern (dobs in Å, (hkl), Ivis) are: 5.45, (110), 25; 2.772, (211), 100; 2.324, (002), 30; 2.254, (301), 20. Luster is adamantine translucent, streak is brownish red; crystals are uniaxial (+) with ω - 2.3, ε - 2.5 at 589 nm. Pleochroism is intense with ε = red orange intense, ω = orange brown. The crystal structure was solved from data collected using synchrotron radiation by traditional direct methods and refined using 350 observed unique reflections to R(F) = 0.037, Rw(F2) = 0.075. The structure of tillmannsite containes isolated tetrahedra (V,As)O4 and tetrahedral clusters (Ag3Hg) formed by metallic atoms. Each (Ag,Hg) metallic atom is coordinated by 3 metallic neighbors and by 3 oxygens.