An Etymological Dictionary of Astronomy and Astrophysics
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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.

Thorium-232 is a → fertile isotope, naturally occurring, from which the → fissile isotope uranium-233 can be bred.

From Thor, the "Scandinavian god of thunder."