title: Redetermination of conichalcite, CaCu(AsO(4))(OH).
abstract: The crystal structure of conichalcite [calcium copper(II) arsenate(V) hydroxide], with ideal formula CaCu(AsO(4))(OH), was redetermined from a natural twinned specimen found in the Maria Catalina mine (Chile). In contrast to the previous refinement from photographic data [Qurashi & Barnes (1963 ▶). Can. Mineral. 7, 561-577], all atoms were refined with anisotropic displacement parameters and with the H atom located. Conichalcite belongs to the adelite mineral group. The Jahn-Teller-distorted [CuO(6)] octa-hedra share edges, forming chains running parallel to [010]. These chains are cross-linked by eight-coordinate Ca atoms and by sharing vertices with isolated AsO(4) tetra-hedra. Of five calcium arsenate minerals in the adelite group, the [MO(6)] (M = Cu, Zn, Co, Ni and Mg) octa-hedron in conichalcite is the most distorted, and the donor-acceptor O-H⋯O distance is the shortest.
authors.affiliation: Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA.
authors.forename: Rachel R
authors.initials: RR
authors.lastname: Henderson
authors.forename: Hexiong
authors.initials: H
authors.lastname: Yang
authors.forename: Robert T
authors.initials: RT
authors.lastname: Downs
authors.forename: Robert A
authors.initials: RA
authors.lastname: Jenkins