Uranium
From dKosopedia
Uranium is the heaviest naturally occurring element and the most common fuel for nuclear fission. Wikipedia provides a general overview. World reserves of uranium are discussed here. The main reserves of uranium in the world are found in (in order of size): Australia, Canada, Kazahkstan, the United States, South Africa, Niger, Brazil and Russia. Geologists believe that Malaysia may also have major uranium reserves due to its similarities geologically to other areas with reserves, but most other major reserves are believed to have already been located.
Depleted uranium is used in U.S. munitions, but the fumes from burning it (the rounds are all designed to burn on impact) are poison gas, illegal under the treaties defining the international laws of war, causing cancer, immune system problems, birth defects, and other illnesses.
Uranium munitions have apparently never been tested by the U.S. for uranyl nitrate emissions, and the scientist responsible for doing so claimed to be unaware that uranium reacts with nitrogen gas (700 deg. C). Uranium contamination has poisoned Baghdad, in part because of their high water table.