Abstract
Abstract. Luxembourgite, ideally AgCuPbBi4Se8, is a new selenide discovered at Bivels, Grand Duchy of Luxembourg. The mineral forms tiny fibres reaching 200 µm in length and 5 µm 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 cm−3. Electron-microprobe analyses indicate an empirical formula Ag1.00(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 R1=0.0476, in the P21∕m space group, with a=13.002(1), b=4.1543(3), c=15.312(2) Å, β=108.92(1)∘, V=782.4(2) Å3, Z=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.
Highlights
The term “Luxembourg” designates a natural region composed of the Grand Duchy of Luxembourg and by the Luxembourg Province in the South of Belgium
Luxembourgite, ideally AgCuPbBi4Se8, is a new selenide discovered at Bivels, Grand Duchy of Luxembourg
A single-crystal structure refinement was performed to R1 = 0.0476, in the P 21/m space group, with a = 13.002(1), b = 4.1543(3), c = 15.312(2) Å, β = 108.92(1)◦, V = 782.4(2) Å3, Z = 2
Summary
The term “Luxembourg” designates a natural region composed of the Grand Duchy of Luxembourg and by the Luxembourg Province in the South of Belgium. The Ardennes mountains are in the north of this region and are named “Oesling” in the Grand Duchy. This massif is constituted of Lower Devonian rocks, mainly schists and quartzites, which were affected by the Variscan metamorphism. The ordering of Cu and Ag at two different crystallographic sites indicated that the mineral was an intermediate member between litochlebite and watkinsonite but a separate mineral species. A part of the type sample used for electron-microprobe analyses is stored in the collection of the Natural History Museum of Luxembourg (catalogue number FD040) Another part of the type used for the single-crystal structure determination is stored in the collection of the Laboratory of Mineralogy, University of Liège, catalogue number 21302. A detailed mineralogical characterisation of this new species is given in the present paper
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