Grimaldiite, a hydroxylate of curomium recognized recently in Yunnan Province of China, occurs mainly in the contact zone of an ultrahasic mass. It differs from Guyanese merumite, a complex mixture of varied chrome mine- rals, in that it has single mineral constituent and although it bears similarity to Guyanese grimaldiite in composition and properties, the latter is present as an interarowth of grimaldiite-mcconnellite. Grimaldiite is of the heterogenite type structure belonging to rhombohe dral system with space group R3m, where a0=2.973±0.004A,c0=13.341±0.02A (according to hexagonal system).Chemical analysis yielded, Cr2O3 70.19, H2O+ 12.72, Al2O3 10.23, Fe203 1.44, TiO2l.15, V2O3 0.16, SiO2 0.72, sum 99.82%， corresnondine to (Cr0.800AL0.167Fe0.013Ti0.012V0.002)0.994OOH. Its refractive index is higher than 1.96, density 3.80, (meas.)3.926 g/cm3 (calc.).