The new mineral species richardsollyite, TlPbAsS3, was discovered in the Lengenbach quarry, Imfeld, Binn Valley, Canton Valais, Switzerland, intimately associated with hutchinsonite and baryte. It occurs as grey-black crystals, up to 750μm, with a metallic lustre. Under
the reflected-light microscope, richardsollyite is grey, with bright-red internal reflections; anisotropy is distinct, with greyish-white to bluish rotation tints. Reflectance values for the four COM wavelengths are [ R
max (%), (l)]: 27.9, 29.8 (471.1
nm); 27.8, 31.0 (548.3 nm); 27.3, 30.8 (586.6 nm); and 27.0, 30.5 (652.3 nm). Electron microprobe analysis gave (in wt%): Tl 34.72(51), Pb 35.45(20), As 12.80(14), Sb 0.04(1), S 16.22(13), total 99.24(47). On the basis of 6 atoms per formula unit, the chemical formula is Tl1.001
Pb1.008 (As1.007 Sb0.002)Σ1.009 S2.982. The main diffraction lines [ d in A (intensity) hkl] are: 4.23 (80) 1 0 2; 3.875 (70) 2 1 1; 3.762 (100) 2 1 0, 1 2 0; 3.278 (70) 1 0 2; 2.931 (70) 0 2 2; 2.714 (70) 1 1 3; and
2.622 (80) 3 1 2. Richardsollyite is monoclinic, space group P 21/ c, with a = 8.8925(2), b = 8.4154(2), c = 8.5754(2) Å, β = 108.665(3)°, V = 607.98(3) Å3, Z = 4. The crystal structure was solved and
refined to R
1 = 0.0242 on the basis of 1590 reflections with F
o >4σ (F
o). It can be described as formed by (1 0 0) [Pb (AsS3)] layers sandwiching Tl+ cations, and is isostructural with synthetic ABCX
(A = K, Rb, Cs; B = Eu, Ba; C = As, Sb; X = S, Se) compounds. The new mineral is named after Richard Harrison Solly (1851–1925) for his outstanding contribution to the knowledge of the Lengenbach mineralogy during the first flourishing period of Lengenbach
investigations, at the beginning of the 20th Century.
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Document Type: Research Article
Publication date: 01 September 2017
This article was made available online on 01 June 2017 as a Fast Track article with title: "Richardsollyite, TlPbAsS3, a new sulfosalt from the Lengenbach quarry, Binn Valley, Switzerland".
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The European Journal of Mineralogy publishes original papers, review articles and letters dealing with the mineralogical sciences s.l. These include primarily mineralogy, petrology, geochemistry, crystallography and ore deposits, as well as environmental, applied and technical mineralogy. Nevertheless, papers in any related field, including cultural heritage, will be considered.
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