Luxembourgite, AgCuPbBi 4Se 8, a new mineral species from Bivels, Grand Duchy of Luxembourg

Philippo, Simon; Hatert, Frédéric; Bruni, Yannick; Vignola, Pietro; Sejkora, Jiří

Luxembourgite, ideally inline-formulaAgCuPbBi4Se8, is a new selenide discovered at Bivels, Grand Duchy of Luxembourg. The mineral forms tiny fibres reaching 200 inline-formulaµm in length and 5 inline-formulaµm in diameter, which are deposited on dolomite crystals. Luxembourgite is grey, with a metallic lustre and without cleavage planes; its Mohs hardness is 3 and its calculated density is 8.00 g cminline-formula−3. Electron-microprobe analyses indicate an empirical formula inline-formulaAg1.00(Cu0.82Ag0.20Fe0.01)Σ1.03Pb1.13Bi4.11(Se7.72S0.01)Σ7.73, calculated on the basis of 15 atoms per formula unit. A single-crystal structure refinement was performed to inline-formulaR1=0.0476, in the inline-formulaP21m space group, with inline-formulaa=13.002(1), inline-formulab=4.1543(3), inline-formulac=15.312(2) Å, inline-formula M13inlinescrollmathml italic β = normal 108.92 ( normal 1 ) 73pt13ptsvg-formulamathimg4d920107eb4a98473050fd7bdaf16dee ejm-32-449-2020-ie00001.svg73pt13ptejm-32-449-2020-ie00001.png , inline-formulaV=782.4(2) Å3, inline-formulaZ=2. The crystal structure is similar to that of litochlebite and watkinsonite and can be described as an alternation of two types of anionic layers: a pseudotetragonal layer four atoms thick and a pseudohexagonal layer that is one atom thick. In the pseudotetragonal layers the Bi1, Bi2 ,Bi3, Pb, and Ag1 atoms are localised, while the Cu2 and Bi4 atoms occur between the pseudotetragonal and the pseudohexagonal layers. Bi1, Bi2, and Bi3 atoms occur in weakly distorted octahedral sites, whereas Bi4 occurs in a distorted 7-coordinated site. Ag1 occupies a fairly regular octahedral site, Cu2 a tetrahedral position, and Pb occurs on a very distorted 8-coordinated site.

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Philippo, Simon / Hatert, Frédéric / Bruni, Yannick / et al: Luxembourgite, AgCuPbBi4Se8, a new mineral species from Bivels, Grand Duchy of Luxembourg. 2020. Copernicus Publications.

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