Abstract
The crystal structure of the rare, spinel-related Sb mineral filipstadite from Langban, Filipstad district, Varmland, Sweden, has been solved and refined in the space group F d 3 ¯ m [ a = 25.9300(6) A, V = 17434.4(5) A3, and Z = 216] and refined to R = 4.41% for 681 F o > 4σ( F o) using Mo K α X-ray data. The structure of filipstadite is topologically identical to the spinel-type structure with cations occupying 1/8 of the tetrahedral (T) and 1/2 of the octahedral (M) interstices of a cubic close-packing of oxygen atoms. Due to the cation ordering, which leads to the tripling of the unit-cell edge, the M and T sites of the spinel-type structure split into six and five independent sites, respectively. Chemical composition was determined by electron microprobe. The fractions of major cations obtained from chemical analysis were distributed between T and M sites taking into account the weighted electron number at both T and M sites, and minimizing the discrepancy between the calculated and the observed overall distance. Cations present in minor amounts were assigned on the basis of their known site preference. The obtained populations (2M = Mn2+0.56Mg0.76Fe3+0.16Al0.02Sb5+0.50; T = Mn2+0.60Mg0.07Fe3+0.30 Zn0.02Si4+0.01) were then tentatively distributed among the individual M and T sites on the basis of crystal chemical considerations.
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