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Does the bazhenovite structure really contain a thiosulfate group? A structural and spectroscopic study of a sample from the type locality

¹ Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via La Pira, 4-I-50121 Firenze, Italy
² Museo di Storia Naturale, Sezione di Mineralogia, Università degli Studi di Firenze, Via La Pira, 4 - I-50121 Firenze, Italy
³ Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia, 3-I-50019 Sesto Fiorentino, Firenze, Italy
⁴ Consorzio Interuniversitario per lo sviluppo dei Sistemi a grande Interfase, Via della Lastruccia, 3-I-50019 Sesto Fiorentino, Firenze, Italy

Correspondence: ^* E-mail: lbindi{at}geo.unifi.it

Bazhenovite was originally reported as a rare, thiosulfate-containing mineral, with the chemical formula CaS₅·CaS₂O₃·6Ca(OH)₂·20H₂O. The structure was predicted to be layered, but no structural details were given. A crystal of "bazhenovite" from the pyritized siderite fragments occurring in the melt products of burning dumps at the type locality in the Chelyabinsk coal basin, South Urals, Russia has been examined by single-crystal X-ray diffraction and vibrational spectroscopy (FTIR and Raman). The structure was solved in space group P2₁/cfinal R_obs = 5.03% (731 reflections) and R_all = 6.98% (966). Although the unit-cell dimensions of the examined crystal [a = 8.391(2), b = 17.346(6), and c = 8.221(4) Å, ß = 119.33(5)°, V = 1043.2(8) ų] match those of the original bazhenovite description [a = 8.45(1), b = 17.47(1), and c = 8.24(1) Å, ß = 119.5°, V = 1059 ų], the thiosulfate group was not detected by either structural analysis or spectroscopic investigations. The structure is an alternating sequence of two kinds of layers, labeled A and B respectively, stacked along [010]. The A layer is the ordered part of the structure and consists of a linkage of Ca(OH)₂(H₂O)₆ antiprisms and Ca(OH)₄(H₂O)₂ octahedra. Taking into account both structural and spectroscopic results, the B layer is inferred to consist of a disordered assemblage of S₃^2–, and to a lesser extent, S₄^2– groups, with the possible presence of additional H₂O and H₂S. The possibility that bazhenovite and the mineral here examined could represent two distinct phases differing slightly from each other with respect to the thiosulfate content is discussed.

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				M. A. Cooper, F. C. Hawthorne, and E. Moffatt Steverustite, Formula(OH)5[Cu+(S6+O3S2-)3](H2O)2, a new thiosulphate mineral from the Frongoch Mine Dump, Devils Bridge, Ceredigion, Wales: description and crystal structure Mineralogical Magazine, August 4, 2009; 73(2): 235 - 250. [Abstract] [Full Text] [PDF]