The Crystal Chemistry of Duftite, PbCuAsO4(OH) and the β-Duftite Problem

Kharisun*, Max R. Taylor, D. J. M Bevan and Allan Pring
Department of Chemistry, The Flinders University of South Australia, GPO Box 2100 Adelaide, S. A. 5001, Australia
Department of Mineralogy, South Australian Museum, North Terrace, S. A. 5000, Australia
*Permanent address: Fakultas Pertanian, Universitas Djenderal Soedirman, P.O. Box 125, Purwokerto 53123, Jawa-Tengah, Indonesia

Abstract: Duftite, PbCu(AsO4)(OH) is orthorhombic, space group P212121 with a = 7.768(1), b = 9. 211(1), c = 5.999(1) Å, Z = 4; the structure has been refined to R = 4.6% and Rw = 6.5% using 640 observed reflections [F> 2σ(F)]. The structure consists of chains of edge-sharing CuO6 ‘octahedra’, parallel to c; which are linked via AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination to form a three dimensional network. The CuO6 ‘octahedra’ show Jahn-Teller distortion with the elongation running approximately along <627>. The hydrogen bonding network in the structure was characterized using bond valence calculations. ‘β-duftite’ is an intermediate in the duftite-conichalcite series, which has a modulated structure based on the intergrowth of the two structures in domains of approximately 50 Å. The origin of the modulation is thought to be associated with displacements in the oxygen lattice and is related to the orientation of the Jahn-Teller distortion of CuO6 ‘octahedra’. Approximately half of the strips show an elongation parallel to <627> while the other strips are elongated parallel to [010]. This ordering results in an increase in the b cell repeat compared to duftite and conichalcite.

Keywords: duftite • conichalcite • crystal structure • crystal chemistry • modulated structure

Mineralogical Magazine; February 1998 v. 62; no. 1; p. 121-130; DOI: 10.1180/002646198547413
© 1998, The Mineralogical Society
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