Structure of Pb‐rich chabournéite from Jas Roux, France

The crystal structure of a specimen of `Pb‐rich' chabournéite from Jas Roux, Hautes‐Alpes, France, with the chemical formula obtained by electron microprobe analysis of Ag0.04 (1)Tl2.15 (2)Pb0.64 (1)Sb5.12 (1)As5.05 (1)S17.32 (5), has been solved by X‐ray single‐crystal diffraction on the basis of 36 550 observed reflections (with Fo > 4σFo) with a final R1 = 0.074. Pb‐rich chabournéite is triclinic P1, with unit‐cell parameters a = 8.5197 (4), b = 42.461 (2), c = 16.293 (8) Å, α = 83.351 (2), β = 90.958 (2), γ = 84.275 (2)°, V = 5823 (3) Å3. Its structural formula is close to [Tl2(Pb0.8Tl0.1Sb1.1)](Sb4.1As4.9)S17, with Z = 8. Its crystal structure is formed by the alternation of two pairs of slabs along the b axis, deriving from the SnS and PbS archetypes, respectively. 104 independent cation sites and 136 S sites occur in the unit cell. Slab interfaces show the alternation, along c, of Tl sites, ninefold coordinated, with Pb, Sb or mixed/split (Pb,Sb) and (Pb,Tl) sites. Within the slabs, 72 independent M3+ sites (M3+ = As, Sb) occur. Considering M3+—S bond distances shorter than 2.70 Å, MS3 triangular pyramidal groups are condensed according to various MmSn chain fragments (`polymers'). The solution of the crystal structure of chabournéite allows its comparison with the closely related homeotypes protochabournéite and dalnegroite.