Meteorite class named after the Ornans meteorite that fell in France in 1868, are related in chemistry and composition to the CV chondrites and may, with them, represent a distinct clan of carbonaceous chondrites that formed in the same region of the early solar system. However, COs are usually blacker and have abundant smaller chondrules (60-70 vol. %; <1 mm in diameter) packed densely within a matrix representing over 70% of the meteorite. The matrix contains magnetite with <1.0 wt. % Cr2O3. CAIs are present but are commonly much smaller and less abundant (8-15 vol. %) than in the CV group. Also typical of COs are small inclusions of Ni-Fe metal that appear as tiny flakes on the polished surfaces of fresh, unweathered samples (1-6 vol. %).
Some or all content above used with permission from J. H. Wittke.