Host: Japan Association of Mineralogical Sciences
Crystal structure of chromian pumpellyite was analyzed using single-crystal X-ray diffraction method in order to investigate behavior of chromium between two independent octahedral sites. The chromian pumpellyite was collected from basic schists in the Osayama ultramafic body, Okayama Prefecture. The Cr distribution is heterogeneous, and maximum Cr2O3 content is 13.3 wt%. The refined occupancies of AlX, CrX, AlY and CrY are 1.50, 0.21, 7.67 and 0.24, respectively. The distribution coefficient of Cr and Al between the X and Y sites [(Cr/Al)X/(Cr/Al)Y] is 3.48 and 1.92, indicating a stronger preference of Cr for the X site. The unit cell parameters are greater than those of Mg-Al-pumpellyite, because of the Al↔Cr substitution. It is consistent with mean Y-O distances.
