Definition of "lanthanum" [lan•tha•num]

• A soft, silvery-white, malleable, ductile, metallic rare-earth element, obtained chiefly from monazite and bastnaesite and used in glass manufacture and with other rare earths in carbon lights for movie and television studio lighting. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,469°C; specific gravity 5.98 to 6.186; valence 3. See Table at element. (noun)

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.

• "Using material mined in past years, Molycorp produces rare-earth elements such as lanthanum, which is used in oil refining, and cerium, used in glass polishing and automotive catalytic converters."
• "A metal oxide complex called lanthanum strontium manganite is ferromagnetic in large quantities."
• "The cost of quotas has become exorbitant for users of lanthanum, which is vital for the catalytic converters that clean the tailpipe pollution of conventional, gasoline-powered cars."