Uranium in unoxidized black ores is tetravalent and in most deposits it occurs as uraninite (an oxide of uranium) and coffinite (a uranium silicate). Pitchblende is a massive, noncrystalline variety of uraninite. The multiple oxides brannerite (oxide of uranium, titanium, thorium, rare earths, and other elements) and davidite (oxide of titanium, iron, and uranium) are the main uranium minerals in a few unoxidized ores. Tetravalent uranium substitutes for thorium and other elements in minerals...