Crystal chemistry of a Cu isotype of makovickyite from the Obari mine, Yamagata Prefecture, Japan

The crystal chemistry of the rare sulfosalt makovickyite from the Obari mine, Yamagata Prefecture, Japan was studied with electron-microprobe analysis (EMPA), and single-crystal X-ray diffraction methods. The chemical composition of the studied crystal is (Cu1.26Ag0.62Pb0.16Bi5.09Sb0.01)S7.13(S8.95Se0.04Te0.01)S9.00 normalized to S(S+Se+Te) = 9 (Z = 2). The structure of this makovickyite (a = 13.2524(5), b = 4.0523(2), c = 14.6775(6) Å, b = 99.487(3)°, V = 777.44(4) Å3, space group C2/m) was refined to R 1 = 4.31 %. Makovickyite, the 4P member of the pavonite homologues, is composed of alternating thick layers of Bi1S6 and Bi2S6 octahedra, and thin layers of Bi3S7 polyhedra alternating with low occupied interstitial tetrahedrally coordinated sub-sites, Cu1, Cu2, Cu3 and Cu3A (in this study). In makovickyite sensu stricto the thin layer also contains a partially occupied octahedral AgS6 site, which was found to be empty in Obari makovickyite. Thus, it is considered a Cu isotype of makovickyite sensu stricto, ideally Ag1.5Bi5.5S9, because the Cu isotype has no significant Ag in the thin layer. The arrangement of the Cu1, Cu2, Cu3, and Cu3A sub-sites is similar as determined for Cu3.21Bi4.79S9, a synthetic 4 P pavonite analogue. The structure of the investigated crystal has 0.5 Ag pfu replacing Bi in the thick layer at Bi1 with the remaining Ag at Bi2.