Thorium is a weakly radioactive metallic chemical element with symbol Th and atomic number 90. Thorium metal is silvery and tarnishes black when it is exposed to air, forming the dioxide; it is moderately hard, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state.

Atomic Weight: 25
Density:       744 g/cm3
Melting Point: 34
Boiling Point: 6543