A soft, ductile, lustrous, silver-white, → radioactive
metal; symbol Th. → Atomic number 90;
→ atomic weight 232.0381;
→ melting point about 1,750 °C;
→ boiling point about 4,790 °C;
→ specific gravity 11.7 at 20 °C.
It was discovered in the mineral thorite (ThSiO4) by the
Swedish chemist Jons Jacob Berzelius in 1828.
It was first isolated by the chemists D. Lely Jr. and L. Hamburger in 1914.
From Thor, the "Scandinavian god of thunder."