Thulium

Thulium, chemical element, symbol Tm; for physical constants see Periodic Table. Thulium was discovered in 1879 by P.T. Cleve in crude erbium oxide. It occurs in the minerals gadolinite, euxenite, ytterspar, and monazite and is obtained commercially from the latter. It is prepared by reducing the anhydrous chloride with calcium. Thulium is a silvery, soft, reactive metal belonging to the series of elements known as the rare-earth metals. Thulium salts have a characteristic absorption spectrum. Ion-exchange and solvent extraction techniques have led to much easier isolation of the rare-earth elements. Thulium and its compounds are used in carbon-arc lighting, glass, and refractory materials.