• journal_title：The Canadian Mineralogist
• Contributor：Dan Topa ; Emil Makovicky
• Publisher：Mineralogical Association of Canada
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.50.2.371
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：50
• issue：2
• firstpage：371
• section：Articles

The crystal structure of eclarite, first determined by Kupčík in 1984, has been refined on material from the scheelite deposit at Felbertal, Salzburg Province, Austria, to an R₁ value of 4.5% on the basis of 4141 unique reflections [F_o > 4σ(F_o)]. The chemical formula of material examined, based on 20.85 large cations (Z = 4) is Cu_0.76Fe_0.45Ag_0.12Pb_8.14Bi_12.59S_27.91; its unit-cell parameters are a 4.0307(1), b 22.7011(6), and c 54.615(1) Å, space group Pmcn. All the principal features of Kupčík’s structure were confirmed. Three cation sites appear split into Pb and Bi subsites, and the octahedral site of the “cosalite-like” fragment is a partially occupied Bi site, flanked by three-fold coordinated, partly occupied Cu1 and Cu2 sites. The tetrahedral (Cu,Fe) site is split into a triangular position and a tetrahedral position. Replacement of Fe by Cu at the tetrahedral site and replacement of Bi by Cu at the octahedral site are positively correlated. They result in a general formula of eclarite equal to Cu_1.5nFe_1−n Pb_9–1.25nBi_12+nS₂₈ in which n is the molar proportion of the copper-based fully substituted ideal end-member Cu_1.5Pb_7.75Bi_13.0S₂₈, and (1–n), that of the Fe-based ideal end-member FePb₉Bi₁₂S₂₈. We propose a new interpretation of the crystal structure of eclarite, as a patchwork of large galenobismutite-like regions joined by interstitial elements.