Kupcikite, Cu3.4Fe0.6Bi5S10, a new Cu-Bi sulfosalt from Felbertal, Austria, and its crystal structure

Kupcikite, Cu 3 . 4 Fe 0 . 6 Bi 5 S 1 0 , a new mineral species, is found in the scheelite deposit of Felbertal, Austria, in a quartz gangue, in association with chalcopyrite, pyrrhotite, molybdenite, sphalerite and native bismuth, intergrown with makovickyite, cupromakovickyite, hodrushite, cuprobismutite and derivatives of the bismuthinite-aikinite series. The mineral is grey with metallic luster, brittle, and without cleavage. Mean micro-indentation hardness is 192 kg/mm 2 (Mohs hardness 3.3), and the calculated density is 6.42 g/cm 3 . In reflected light, it is grayish white; the anisotropy is moderate in air and strong in oil, and it does not show internal reflections. Reflectance values (in %) in air are, for R 1 and R 2 , 33.55, 40.56 at 470 nm, 33.92, 41.14 at 546 nm, 34.16, 41.35 at 589 nm, and 34.2, 41.32 at 650 nm. The average results of seven electron-microprobe analyses are: Cu 13.02, Fe 2.23, Ag 0.11, Cd 0.3, Bi 64.21, Sb 0.12, S 20.10, total 100.08 wt. %, corresponding to Fe 0 . 6 4 Cu 3 . 2 9 Ag 0 . 0 1 5 Cd 0 . 0 4 5 Sb 0 . 0 1 5 Bi 4 . 9 4 S 1 0 . 0 7 (basis: 19 atoms per formula unit). The simplified formula, in accordance with the crystal-structure analysis, is Fe 0 . 6 Cu 3 . 4 Bi 5 S 1 0 . The crystal structure was solved, to R = 4.1%, from single-crystal data obtained on a four-circle diffractometer with an area detector. Kupcikite has a monoclinic cell with a 17.512(2), b 3.9103(4), c 12.869(1) A, β 108.56(1)°, V835.4(1) A 3 , space group C2/m, with Z = 2. The strongest lines in the calculated powder-diffraction pattern [d in A (I)(hkl)] are: 6.028(4)(201), 3.596(7)(401), 3.213(4)(204), 3.128(10)(112), 3.071(7)(312), and 2.683(5)(113). Its structure corresponds to the structure of synthetic Cu 4 Bi 5 S 1 0 ; the (Cu,Fe) position in the mineral is distinctly split. Kupcikite is closely structurally related to cuprobismutite and hodrushite. It is the N = 1 member of the cuprobismutite series, whereas cuprobismutite is the N = 2 member. Hodrushite is composed of a regular 1:1 intergrowth of kupcikite-like and cuprobismutite-like layers. In typical intergrowths with makovickyite or hodrushite, kupcikite shows sharp straight boundaries with both of these phases, but where in contact with derivatives of the bismuthinite-aikinite series, the latter replace kupcikite. In a rare occurrence of kupcikite with cuprobismutite in the same aggregate, the cuprobismutite is replaced by kupcikite. obtenues sur monocristal avec un diffractometre a quatre cercles et un detecteur de type CCD. La kupcikite possede une maille monoclinique, a 17.512(2), b 3.9103(4), c 12.869(1) A, β 108.56(1)°, V 835.4(1) A 3 , groupe spatial C2/m, avec Z = 2. Les six raies les plus intenses du spectre de diffraction calcule [d en A (1)(hkl)] sont: 6.028(4)(201), 3.596(7)(401), 3.213(4)(204), 3.128(10)(112), 3.071(7)(312), et 2.683(5)(113). Sa structure correspond a celle du compose synthetique Cu 4 Bi 5 S 1 0 ; la position (Cu,Fe) du mineral, par contre, est distinctement scindee. La kupcikite montre une relation structurale etroite avec la cuprobismutite et la hodrushite. Elle est l'homologue N = 1 de la serie de la cuprobismutite, tandis que la cuprobismutite en est le membre ayant N egal a 2. La hodrushite est composee d'une intercroissance reguliere 1:1 de couches de type kupcikite et cuprobismutite. Dans les intercroissances typiques avec la makovickyite ou la hodrushite, la kupcikite fait preuve d'interfaces rectilignes et franches avec ces deux phases, mais en contact avec les derives de la serie de la bismuthinite-aikinite, ces derniers la remplacent. Dans un rare exemple de kupcikite avec cuprobismutite dans le meme aggregat, la cuprobismutite se voit remplacee par la kupcikite.