Abstract
Crystal structure of shuiskite from Sarani, Ural was refined by using X-ray Rietveld method. The chemical compositions are as follows: CaO 21.0-22.2 wt%, MgO2.8-3.8 wt%, Cr2O3 12.9-16.3 wt%, Al2O3 14.7-17.0 wt%, total Fe2O3 0.0-0.4 wt%, and SiO2 34.3-36.4 wt% (n=23). The unit-cell parameters are refined as a = 8.8155(2)A, b = 5.9371(2)A, c=19.1528(4)A, beta = 97.608(2)deg., and V = 993.61(4)A3. Cation distributions of the octahedral X and Y sites are Mg0.44Al0.32Cr0.24 and Al0.75Cr0.25, respectively. Thus, the interpretation of ivanov et al. (1981) that Cr cations are distributed only at the Y sites is wrong, and cr cations must be assigned to both the X and Y sites.
