Structure of Pb-rich chabournéite from Jas Roux, France

Abstract

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 Ag(0.04 (1))Tl(2.15 (2))Pb(0.64 (1))Sb(5.12 (1))As(5.05 (1))S(17.32 (5)), has been solved by X-ray single-crystal diffraction on the basis of 36,550 observed reflections (with F(o) > 4σF(o)) 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) Å(3). Its structural formula is close to [Tl2(Pb(0.8)Tl(0.1)Sb(1.1))](Sb(4.1)As(4.9))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 M(3+) sites (M(3+) = As, Sb) occur. Considering M(3+)-S bond distances shorter than 2.70 Å, MS3 triangular pyramidal groups are condensed according to various M(m)S(n) chain fragments (`polymers'). The solution of the crystal structure of chabournéite allows its comparison with the closely related homeotypes protochabournéite and dalnegroite.

Lead-antimony sulfosalts from Tuscany (Italy). XVIII. New data on the crystal-chemistry of boscardinite

“…respectively. This would confirm that the use of the R Tl,S bond-valence parameter by Brese and O'Keeffe (1991) for mixed (Tl,Pb) results in an overestimation of Pb, as discussed by Biagioni et al (2015) for chabournéite and protochabournéite.…”

“…Considering only the four shortest distances, the average <Sb9a-S> distances are 2.646 Å in both the crystal structures. The same configuration occurs in chabournéite from Jas Roux (Biagioni et al, 2015), but the higher As/(As+Sb) at. ratio with respect to protochabournéite favours the As-to-Sb substitution at the isolated trigonal pyramids, as observed in (Tl,As)-enriched boscardinite with respect to type boscardinite, or to possible mean positions (Sb10a -see below).…”

Modular Crystal Chemistry of Thallium Sulfosalts

“…That explains the doubts arising from centrosymmetricity tests: they This mineral is homeotypic with chabournéite, which has doubled a and c parameters. Substructure of chabournéite was described by Nagl [83], full structure by Biagioni et al [84]. Dalnegroite [85] also has doubled a and c parameters.…”

“…In the potential 'chabournéite composition field' [82], protochabournéite, with the composition of the structurally investigated sample Tl 1.70 Pb 1.60 (Sb 8.80 As 0.90 ) Σ9.70 S 17 , is the Sb-rich phase, with the Sb/ (Sb + As) ratio centered on 0.8-0.9 and the Pb/(Pb + 2Tl) ratio centered on 0.24-0.30. At least preliminarily, chabournéite is defined as Sb/(Sb + As) = 0.50 to 0.60 [84], however, the 'Pb-character' of it lies between Pb-free (approximately (Tl 2.5 Sb 2.5 )(Sb 4 As 5 )S 17 ) and Pb-rich, with Pb/(Pb + 2Tl) up to 0.23, and with the Sb/(Sb + As) ratio reaching almost 0. 3 .…”

“…In some of these structures (e.g., écrinsite), this set is differentiated into Tl-rich positions and Tl-poor positions. Such differentiation is pronounced especially for the homeotypic chabournéite family [82][83][84][85][86][87][88]. When stoichiometry requires, the prism columns host Tl-Sb sequencies.…”