The structure of antimonian dussertite, Ba(Fe (super 3+) (sub 0.84) , Sb (super 5+) (sub 0.16) ) 3 (AsO 4 ) 2 (OH,H 2 O) 6 , has been refined in space group R3m with a 7.410(3), c 17.484(4) Aa, Z = 3, to R = 3.2% and R w = 3.7% using 377 observed reflections with I> or =3 sigma (I). The structure is of the alunite-type and consists of sheets of corner-sharing (Fe (super 3+) , Sb (super 5+) )O 6 octahedra parallel to (0001). The substitution of Sb (super 5+) for Fe (super 3+) , and not for As (super 5+) , 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 AsO 4 tetrahedra and six O atoms from the (Fe (super 3+) ,Sb (super 5+) )O 6 octahedra. The mean bond lengths for the various coordination polyhedra are As-O 1.684(3) Aa, (Fe,Sb)-O 2.004(1) Aa, and Ba-O 2.872(2) Aa. 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.

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