Rudabányaite, a new mineral with a [Ag<sub>2</sub>Hg<sub>2</sub>]<sup>4+</sup> cluster cation from the Rudabánya ore deposit (Hungary)

Herta Silvia Effenberger, Sándor Szakáll, Béla Fehér, Tamás Váczi, Norbert Zajzon

Rudabányaite was found in cavities of siliceous sphaerosiderite and limonite rocks at the Adolf mine area of the Rudabánya ore deposit (North-East Hungary). The new mineral forms small crystals up to 0.6 mm and aggregates of a few mm across. Usually they have a xenomorphic shape, only occasionally cubic symmetry is morphologically discernible; the crystal forms {110} and {100} were recognized. The crystals are transparent, have yellowish-orange to brownish-yellow colour and a lemon-yellow streak, the lustre is adamantine. The Mohs’ hardness is 3-4. No cleavage was observed. Rudabányaite is optically isotropic. The density could not be measured due to lack of material; ?(calc.) = 8.04 g/cm3. Electron-microprobe analyses gave the average composition (in wt%) Ag2O 29.39, Hg2O 52.62, As2O5 13.69, Cl 4.62, SO3 0.19, O=Cl -1.04, sum 99.47. The empirical formula based on four oxygen atoms is (Ag2.06Hg2.05)S=4.11(As0.97S0.02)S=0.99O4Cl1.06; the idealized formula as derived from chemical analyses and crystal-structure investigation is [Ag2Hg2][AsO4]Cl. The crystal-structure investigation was performed on single-crystal X-ray data; the refinements on F2 converged at wR2(F2) = 0.068 and R1(F) = 0.031 for all 972 unique data and 53 variable parameters. Rudabányaite crystallizes in space group F4¯3c?, a = 17.360(3) Å, V = 5231.8 Å3, Z = 32. The crystal structure is characterised by two crystallographically different [M4]4+ cluster cations forming tetrahedra; M = (Ag,Hg) with a ratio Ag:Hg ~ 1:1. There is not any evidence for an order between the Ag and Hg atoms. Small amounts of the M atoms are displaced by ~0.5 Å. Topologically, the barycentres of the [M4]4+ clusters and the As atom positions of the crystal structure of rudabányaite form a cubic primitive lattice with a' = ½a = 8.68 Å; half of the voids are occupied by Cl atoms.

Institut für Mineralogie und Kristallographie
Externe Organisation(en)
Herman Ottó Museum, Hungarian Academy of Sciences, University of Miskolc, Eötvös Loránd University Budapest
European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
Anzahl der Seiten
ÖFOS 2012
Kristallographie, Mineralogie
Link zum Portal