It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis. Uranium has sixteen isotopes, all of which are radioactive. The US DOE has adopted the value of 0.711 as being their official percentage of 235U in natural uranium.
Natural uranium is sufficiently radioactive to expose a photographic plate in an hour or so.
Much of the internal heat of the earth is thought to be attributable to the presence of uranium and thorium. The origin of uranium, the highest member of the naturally occurring elements - except perhaps for traces of neptunium or plutonium, is not clearly understood. However it may be presumed that uranium is a decay product of elements with higher atomic weight, which may have once been present on earth or elsewhere in the universe. These original elements may have been formed as a result of a primordial creation, known as the big bang, in a supernova, or in some other stellar processes. Uses Uranium is of great importance as a nuclear fuel.