Redetermination of olivenite from an untwinned single-crystal.

The crystal structure of olivenite, ideally Cu(2)(AsO(4))(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu(2)(As(0.92)P(0.08)O(4)), from Majuba Hill (Nevada, USA). Olivenite is structurally analogous with the important rock-forming mineral andalusite, Al(2)OSiO(4). Its structure consists of chains of edge-sharing, distorted [CuO(4)(OH)(2)] octa-hedra extending parallel to [001]. These chains are cross-linked by isolated AsO(4) tetra-hedra through corner-sharing, forming channels in which dimers of edge-sharing [CuO(4)(OH)] trigonal bipyramids are located. The structure is stabilized by medium to weak O-H⋯O hydrogen bonds. In contrast to the previous refinements from powder and single crystal X-ray data, all non-H atoms were refined with anisotropic displacement parameters and the H atom was located.