Iranite, CuPb₁₀(CrO₄₎₆(SiO₄₎₂(OH) ₂, isomorphous with hemihedrite

This study presents the first structural report of iranite, ideally CuPb10(CrO4)6(SiO4)2(OH)2 [copper deca-lead hexa-chromate bis-(orthosilicate) dihydroxide], based on single-crystal X-ray diffraction data. Iranite is isomorphous with hemihedrite, with substitution of Cu for Zn and OH for F. The Cu atom is situated at the special position with site symmetry . The CrO4 and SiO4 tetra-hedra and CuO4(OH)2 octa-hedra form layers that are parallel to (120) and are linked together by five symmetrically independent Pb²⁺ cations displaying a rather wide range of bond distances. The CuO4(OH)2 octa-hedra are corner-linked to two CrO4 and two SiO4 groups, while two additional CrO4 groups are isolated. The mean Cr - O distances for the three nonequivalent CrO4 tetra-hedra are all slightly shorter than the corresponding distances in hemihedrite, whereas the CuO4(OH)2 octa-hedron is more distorted than the ZnO4F2 octa-hedron in hemihedrite in terms of octa-hedral quadratic elongation.