• journal_title：The Canadian Mineralogist
• Contributor：Luca Bindi ; Yves MOËLO ; Philippe Léone ; Michel Suchaud
• Publisher：Mineralogical Association of Canada
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.50.2.471
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：50
• issue：2
• firstpage：471
• section：Articles

Arsenopyrite from La Roche-Balue quarry (Loire-Atlantique department, France), with the stoichiometric composition FeAsS, has been studied by X-ray single-crystal diffraction and ⁵⁷Fe Mössbauer spectroscopy. Its unit cell is a 5.7612(8), b 5.6841(7), c 5.7674(8) Å, β 111.721(8)°, and V 175.46(4) ų (Z = 4). Taking into account very fine ubiquitous twinning on {101}, its crystal structure has been refined in the space group P2₁/c on the basis of 758 unique reflections [F_o > 4σ(F_o)] to R₁ = 0.0298. Within uncertainty limits, it indicates three unmixed Fe, As and S positions. The ⁵⁷Fe Mössbauer spectrum of this arsenopyrite shows two broad absorption peaks that were fitted using the superposition of three doublets denoted as A, B and C, with parameters relative to area S, isomer shift δ, and quadrupole splitting ΔE_Q, as follows: S_A 82.2%, δ_A 0.24(1) mm/s, ΔE_QA 1.12(2) mm/s; S_B 8.5%, δ_B 0.25(1) mm/s, ΔE_QB 0.69(2) mm/s; S_C 9.3%, δ_C 0.26(1) mm/s, ΔE_QC 1.49(2) mm/s. This set of values agrees well with the most recently published results for arsenopyrite samples with a composition close to stoichiometry. The three distinct Fe positions indicated by Mössbauer spectroscopy are not visible in the X-ray study. Whereas the main doublet A would seem to correspond to the FeAs₃S₃ octahedron of the ideal structure, the two minor doublets B and C, with a ΔE_Q shift towards marcasite and löllingite, respectively, may be due to local disorder (e.g., twin contact walls) changing the octahedral coordination of Fe to unequal As:S ratios.