Thorium is a Chemical element with the symbol Th and the Atomic number 90. It is naturally occurring and slightly radioactive. Thorium is a pure, silvery-white metal that retains luster for several months. Thorium can slowly tarnish in the air when exposed to oxygen. This process is oxidation, similar to that of the rusting of iron, but instead of forming Iron-oxide (rust), it forms Thorium dioxide. Thorium dioxide has the highest Melting point of all the oxides. Thorium is also an actinide. It is an alternative fuel in nuclear energy to Uranium. Thorium was also named after Thor, the Norse god of Thunder.