This study presents the first structural report of a natural cobaltaustinite sample (calcium cobalt arsenate hydroxide) based on single-crystal X-ray diffraction data. Cobaltaustinite, with the ideal formula CaCo(AsO4)(OH), belongs to the adelite mineral group. The CoO 6 octahedra share edges to form chains extending parallel to the c axis, which are cross-linked by Ca2+ ions and by sharing vertices with isolated AsO4 tetrahedra. The Ca2+ ions are situated in square antiprisms formed by eight O atoms. The major structural difference between the five calcium arsenates in the adelite group is shown in the bonding environments around the octahedrally coordinated M2+ cations (M = Cu, Zn, Co, Ni and Mg), with the average M-O distance decreasing from Cu-O in conichalcite, CaCu(AsO4)(OH) to Zn-O in austinite, CaZn(AsO 4)(OH), Co-O in cobaltaustinite, Ni-O in nickelaustinite, CaNi(AsO4)(OH), and Mg-O in adelite, CaMg(AsO4)(OH). The donor-acceptor O-H⋯O distance [2.721 (7) Å] in cobaltaustinite is similar to those in austinite and nickelaustinite, but different from those in adelite and conichalcite.
|Original language||English (US)|
|Journal||Acta Crystallographica Section E: Structure Reports Online|
|State||Published - Feb 2007|
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics