Original paper

Felbertalite, Cu2Pb6Bi8S19, a new mineral species from Felbertal, Salzburg Province, Austria

Topa, Dan; Makovicky, Emil; Criddle, Alan J.; Paar, Werner H.; Balič-Žunić, Tonči

Abstract

Felbertalite, a new copper-lead-bismuth-sulphosalt, has been found in quartz veins, in the scheelite deposit Felbertal, Salzburg Province, Austria. It occurs as rare elongated crystals, up to 0.5 mm long and 0.2 mm in diameter. The mineral is always in contact with Ag-bearing lillianite and a Se-free junoite-like mineral. Associated minerals are: cosalite, galenobismutite, members of the bismuthinite-aikinite series, galena, native Bi and traces of chalcopyrite. Felbertalite is opaque, with metallic lustre and greyish-black streak. In reflected light, it has a white colour with distinct anisotropy and perceptible bireflectance in air and oil and without internal reflections. Reflectance data and colour values are supplied. Mohs hardness is 3.3-3.4, according to a microhardness VHN25 of 197-216 kg/mm2. The mean of 15 electron-microprobe analyses is: Cu 3.56, Ag 1.02, Pb 30.10, Cd 0.38, Bi 48.3, Te 0.23, S 16.76, total 100.36 wt.%, from which a simplified formula Cu2Pb6Bi8S19 (on the basis of 35 atoms) can be derived. The mineral has a monoclinic unit cell with a = 27.637(4), b = 4.0499(6), c = 20.741(3) Å, β = 131.258(2)o, V = 1745.1(7) Å3, a:b:c = 6.82:1:5.12, Z = 2, space group C2/m. The calculated density is Dcalc = 6.948 g/cm3. The strongest five lines in the X-ray powder pattern [d in Å, (I), (hkl)] are: 2.904 (100) (510), 3.758 (88) (203, 111, 11-2), 3.379 (77) (40-6, 80-3,112), 3.496 (62) (31-3), 3.432 (45) ( 60-6). Felbertalite is a homologue of junoite. The synthetic AG-phase of Mariolacos (1979) can tentatively be interpreted as synthetic felbertalite. The name is given after the valley of Felbertal where the mine is located.

Keywords

felbertalitenew mineralcu-pb-bi-sulphosaltx-ray datajunoite homologous series