While uranium is one of the most abundant elements in the Earth's crust, concentrated uranium ores are found in only a few places, usually in hard rock, such as granites or consolidated sediments, such as sandstone.

Uranium is commonly found as the mineral uraninite or pitchblende, a form of uraninite mixed with other minerals. It is usually black to steel black with a dull lustre. The most stable form is Triuranium octoxide (U3O8), better known as yellowcake, which is the concentrate most commonly derived from uranium mining operations.