gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199548277 The Structure of Antimonian Dussertite and the Role of Antimony in Oxysalt Minerals Kolitsch U. 1 Slade P. G. 2 Tiekink E. R. T. 3 Pring A. 1 Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, S. A. 5000, Australia CSIRO Land and Water, Private Bag No. 2, Glen Osmond, S. A. 5064, Australia Department of Chemistry, The University of Adelaide, Australia 5005 2 1999 63 1 17 26 1 5 1998 1 7 1998 Copyright © 1999, The Mineralogical Society 1999 Abstract

The structure of antimonian dussertite, Ba(Fe0.843+,Sb0.165+)3(AsO4)2(OH,H2O)6, has been refined in space group R¯3m with a 7.410(3), c 17.484(4) Å, Z = 3, to R = 3.2 % and Rw = 3.7 % using 377 observed reflections with I ⩾ 3 σ(I). The structure is of the alunite-type and consists of sheets of corner-sharing (Fe3+,Sb5+)O6 octahedra parallel to (0001). The substitution of Sb5+ for Fe3+ and not for As5+, is unambiguously demonstrated not only by the structure refinement but also by electron microprobe analyses and crystal-chemical considerations. The icosahedrally coordinated Ba cations occupy cavities between pairs of octahedral sheets and are surrounded by six O atoms from the AsO4 tetrahedra and six O atoms from the (Fe3+,Sb5+)O6 octahedra. The mean bond lengths for the various coordination polyhedra are As-O 1.684(3) Å, (Fe,Sb)-O 2.004(1) Å,, and Ba-O 2.872(2) Å. A hydrogen-bonding network is modelled using bond-valence calculations. The dussertite sample investigated is the first member of the crandallite group found to contain substantial Sb.

 Keywords dussertite crystal structure crystal chemistry antimony crandallite group