n. A lustrous, iron-gray, malleable metallic rare-earth element that occurs chiefly in the minerals monazite and bastnaesite, exists in four allotropic states, is a constituent of lighter flint alloys, and is used in various metallurgical and nuclear applications. Atomic number 58; atomic weight 140.12; melting point 795°C; boiling point 3,468°C; specific gravity 6.67 to 8.23; valence 3, 4. See Table at element.