1">The crystal structure of eclarite, first determined by 13-1" class="xref-bibr" href="#ref-13">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 [Fo > 4σ(Fo)]. The chemical formula of material examined, based on 20.85 large cations (Z = 4) is Cu0.76Fe0.45Ag0.12Pb8.14Bi12.59S27.91; 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 Cu1.5nFe1−n Pb9–1.25nBi12+nS28 in which n is the molar proportion of the copper-based fully substituted ideal end-member Cu1.5Pb7.75Bi13.0S28, 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.
