Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Jiří Sejkora, Daniela Mauro, Cristian Biagioni

Single-crystal structure refinement of bukovite, (Cu₃Fe)_Σ4Tl₂Se₄

Journal of Geosciences, volume 68 (2023), issue 3, 179 - 184

DOI: http://doi.org/10.3190/jgeosci.373

Single-crystal X-ray diffraction study of bukovite, ideally (Cu₃Fe₁)_Σ4Tl₂Se₄, was performed using a specimen from the Ústaleč uranium deposit, 15 km west of Horažďovice, SW Bohemia, Czech Republic. In the studied specimens, bukovite occurs in calcite gangue with uraninite associated with bytízite, chaméanite, 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 (Cu_3.06Fe_0.97)_Σ4.03Tl_1.97(Se_3.91S_0.09)_Σ4.00 (Z = 1). Unit-cell parameters are a = 3.9694(8), c = 13.694(3) Å, V = 215.77(10) ų, space group I4/mmm. The crystal structure was refined by single-crystal X-ray diffraction data to R₁ = 0.0264 for 92 unique reflections with F_o > 4σ(F_o) and 10 refined parameters. The crystal structure of bukovite can be described as formed by single 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)_Σ4Tl₂Se₄ is proposed.