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Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 Editors: W. Clegg and D. G. Watson
Cobaltaustinite, CaCo(AsO4)(OH) Hexiong Yang, Gelu Costin, John Keogh, Ren Lu and Robert T. Downs
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Acta Cryst. (2007). E63, i53–i55 Yan g et al. ¯ CaCo(AsO4)(OH) inorganic papers
Acta Crystallographica Section E Cobaltaustinite, CaCo(AsO )(OH) Structure Reports 4 Online ISSN 1600-5368
Hexiong Yang,* Gelu Costin, This study presents the first structural report of a natural Received 30 December 2006 John Keogh, Ren Lu and cobaltaustinite sample (calcium cobalt arsenate hydroxide) Accepted 19 January 2007 Robert T. Downs based on single-crystal X-ray diffraction data. Cobaltaustinite, with the ideal formula CaCo(AsO4)(OH), belongs to the University of Arizona, Department of adelite mineral group. The CoO6 octahedra share edges to Geosciences, 1040 East 4th Street, Tucson, form chains extending parallel to the c axis, which are cross- AZ 85721-0077, USA 2+ linked by Ca ions and by sharing vertices with isolated AsO4 2+ Correspondence e-mail: [email protected] tetrahedra. The Ca 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 Key indicators coordinated M2+ cations (M = Cu, Zn, Co, Ni and Mg), with Single-crystal X-ray study the average M—O distance decreasing from Cu—O in T = 273 K Mean (Co–O) = 0.005 A˚ conichalcite, CaCu(AsO4)(OH) to Zn—O in austinite, R factor = 0.045 CaZn(AsO4)(OH), Co—O in cobaltaustinite, Ni—O in wR factor = 0.078 nickelaustinite, CaNi(AsO4)(OH), and Mg—O in adelite, Data-to-parameter ratio = 16.8 CaMg(AsO4)(OH). The donor–acceptor O—H O distance [2.721 (7) A˚ ] in cobaltaustinite is similar to those in austinite For details of how these key indicators were automatically derived from the article, see and nickelaustinite, but different from those in adelite and http://journals.iucr.org/e. conichalcite.
Comment More than a dozen minerals belong to the adelite group, which
crystallize in the orthorhombic space group P212121 (Qurashi & Barnes, 1963, 1964) and have the general formula
Figure 1 The crystal structure of cobaltaustinite. Ca2+ cations are drawn with anisotropic displacement ellipsoids at the 99% probability level and H # 2007 International Union of Crystallography atoms as spheres of arbitrary radii. Hydrogen bonding is indicated by All rights reserved green lines.