Crystal and absolute structure of enargite from Bor (Serbia)
Karanović, L.j.; Cvetković, L.j.; Poleti, D.; Balićž
published: Jun 18, 2002
Crystal structure of enargite, Cu3AsS4, from locality Bor (Serbia) has been refined using single-crystal data (Mo-Kα X-ray diffraction, CCD area detector). The chemical composition of the sample determined by Energy Dispersive Spectrometry is Cu3.074As0.955S3.97. In the polished section, enargite occurs in tabular grains and short prismatic crystals. Colour of the reflected light is brownish-gray with a slight purplish tint. The space group of enargite is Pmn21 with a = 7.4127(16), b = 6.4404(15), c = 6.1577(14) Å and Z = 2. The refinement by full-matrix least-squares on F2 involving anisotropic displacement parameters for all atoms led to a discrepancy factor R1 = 0.0329 for 351 unique reflections with F > 4σ(F). The absolute structure was also determined and confirmed by the Flack parameter calculation. The structure is derived from wurtzite by ordered cation substitution. Each cation is tetrahedraly coordinated to four sulfur atoms and each sulfur is tetrahedraly coordinated by one arsenic and three copper atoms. Observed differences in Cu-S bonds are discussed in view of cation ordering and distortions of tetrahedra are analyzed.