Abstract
The occurrence, mineral assemblages, and chemical compositions of chromian minerals in basic schist in the Osayama ultramafic body, Okayama Prefecture, were investigated. Chromian minerals occur in basic schist blocks in the Osayama ultramafic body. Chromian pumpellyite grains occur as pseudomorphs after primary minerals. They are colorless and are twinned. The Cr distribution is extremely heterogeneous due to substitution of Cr for Al, and Cr2O3 content reach 13.3 wt%. Fe distribution is relatively homogeneous. The chemical formula of the chromian pumpellyite is calculated to be: (K0.02Na0.19Ca7.85)&Shigma;8.06(Mn2+0.05Fe2+0.35Mg1.71Cr1.10Al0.73)&Shigma;3.94(Cr2.36V0.01Al5.63)&Shigma;8.00(Al0.19Si11.81)&Shigma;12.00O41.01(OH)14.99. The bulk composition of the basic schist blocks in the serpentinite melange suggests that its protolith was picritic basalt which included chromite.
