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.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.