Thorium

Thorium, chemical element, symbol Th; for physical constants see Periodic Table. Discovered by Jöns Jakob Berzelius in 1828. The element occurs in the minerals thorite, thorianite, orangite, yttrocrasite, and monazite and is obtained commercially from the latter. Thorium is obtained as a powder by reduction of its oxide with calcium. It is a gray-white, radioactive metal. It is pyrophoric in powder form and burns in air to form the oxide, which has the highest melting point of all oxides. It is a member of the actinide series. Thorium is used as a nuclear fuel source and for incandescent lamp mantles. It is estimated that the energy available from thorium in the earth's crust is probably greater than that from uranium and fossil fuels combined.