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 such a monazite, uranothorite, multiple oxides of niobium, and tantalum, and for calcium in carbonate fluorapatite. It also occurs in unidentified organic compounds in many coaly rocks and marine black shales.

Under oxidizing conditions tetravalent uranium changes to hexavalent uranium and forms oxide, vanadate, arsenate, silicate, sulfate, and carbonate compounds, most of which are hydrous and many of which are bright yellow or green. Carnotite (potassium uranium vanadate) and tyuyamunite (calcium uranium vanadate) are the most common and abundant. Other common minerals include uranophane (a hydrous silicate) and metuzeunerite (an arsenate).