Uranium
Uranium is a metal which naturally occurs in various different minerals. It can be mined out of any uranium-bearing ores. The mined form is not useful to us and must be chemically altered to what is called "yellow cake" so we can use it to get nuclear energy. It is a heavy metal with a silvery-white color. While it is pretty hard, it is actually slightly softer than steel. It has many isotopes which aid in it's greatest importance being through it's use as a nuclear fuel. This is done through a reaction between various uranium isotopes. They can be purified in different ways too, such as gaseous diffusion, a centrifuge, or laser enrichment. The process and different isotopes used determine the final results.