Single-crystal structure refinement of bukovite, (Cu3Fe)∑4Tl2Se4

Single-crystal X-ray diffraction study of bukovite, ideally (Cu3Fe)sigma 4Tl2Se4, was performed using a specimen from the ustale & ccaron; uranium deposit, 15 km west of Horazd'ovice, SW Bohemia, Czech Republic. In the studied specimens, bukovite occurs in calcite gangue with uraninite associated with bytizite, chameanite, clausthalite, hakite-(Hg) and umangite. Electron microprobe analysis gave (in wt. % - average of 20 spot analyses): Cu 19.90, Tl 41.21, Fe 5.55, S 0.31, Se 31.60, total 98.57. On the basis of 10 atoms per formula unit, the empirical formula of bukovite is (Cu3.06Fe0.97)sigma 4.03 Tl1.97(Se3.91S0.09)sigma 4.00 (Z = 1). Unit-cell parameters are a = 3.9694(8), c = 13.694(3) angstrom, V = 215.77(10) angstrom 3, space group I4/mmm. The crystal structure was refined by single-crystal X-ray diffraction data to R1 = 0.0264 for 92 unique reflec-tions with Fo mackinawite-like {001} layers of edge-sharing (Cu,Fe)-centered tetrahedra, with Tl atoms hosted in eight-fold cubic coordinated sites intercalated between these tetrahedral layers. The role of Fe is discussed and the chemical formula (Cu3Fe)sigma 4Tl2Se4 is proposed.