Chemistry of chromian spinel in picrite sill from Ogi, Sado island, Niigata Prefecture, Japan

Chromian spinels occur in two textural forms in picrite sill intruded in Neogene volcanic rocks, from Ogi at the southwestern end of the Sado island, Niigata Prefecture. Small (/ (Cr+Al+Fe^) atomic ratio of chromian spinel is lower than 0.2. The molecule proportion of spinel is more than about 40 %. The sum of the molecule proportions of spinel, chromite and magnesio-chromite is beyond 90 %. The formula of the common chromian spinel was given as (Mg_Fe^_Mn_)_ (Ti_Al_Cr_Fe^_)_O_