• journal_title：The Canadian Mineralogist
• Contributor：Dan Topa ; Emil Makovicky ; Tonc̀i Balić-Žunić
• Publisher：Mineralogical Association of Canada
• Date：2008-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.46.2.515
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：46
• issue：2
• firstpage：515
• section：Articles

The crystal structure of cupromakovickyite, ideally Cu₈Pb₄Ag₂Bi₁₈S₃₆, from the skarn deposit at Băiţa Bihor, in Romania, has been solved by direct methods and refined to an R₁ index of 5.36% for 2680 unique reflections measured with MoKα radiation on a four-circle diffractometer equipped with a CCD detector. Cupromakovickyite has a monoclinic cell with a 13.405(8), b 4.016(3), c 29.949(19) Å, β 99.989(16), V 1587.8(17) ų, space group C2/m and Z = 1. There are eight metal sites and twelve sulfur sites in each of the four asymmetric units. The thicker, galena-like layers are composed of parallel chains Bi4–Bi1–Bi1–Bi4 four octahedra long. In the thinner layers, the octahedra of Ag are replaced by two tetrahedrally coordinated Cu sites, whereas one of the paired square pyramids of Bi is replaced by Pb. The asymmetry of the thin layer is responsible for the doubling of the c parameter for cupromakovickyite with respect to makovickyite. To be able to compare them, the crystal structure of Cu-bearing makovickyite, Cu_2.25Ag_1.56 (Pb_0.27Cd_0.13)_{∑ 0.4}Bi_10.46S₁₈, from a scheelite deposit at Felbertal, in Austria, has been refined to an R₁ index of 4.36% for 1320 unique reflections measured with the same equipment. Makovickyite has a monoclinic cell with a 13.239(3), b 4.0547(7), c 14.667(3) Å, β 99.397(4), V 776.7(3) ų, space group C2/m and Z = 1. There are four metal sites and six sulfur sites in each of the four asymmetric units. The thicker, galena-like layers are composed of parallel chains Bi2–Bi1–Bi1–Bi2 four octahedra long. In the thinner layers, the octahedra of Ag are partially replaced by two tetrahedrally coordinated Cu sites.