Definition of "thulium" []

• A bright, silvery rare-earth element obtained commercially from monazite, having an x-ray emitting isotope that is used in small portable medical x-ray units. Atomic number 69; atomic weight 168.934; melting point 1,545°C; boiling point 1,727°C; specific gravity 9.3; valence 2, 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.

• "China accounts for 95 percent of global production and about 60 percent of consumption of rare metals, including dysprosium, terbium, thulium, lutetium and yttrium, according to the U.S."
• "Now Appearing: The mysterious element thulium skip to main"
• "Rare-earth elements include the relatively common cerium, used in pollution-control equipment, and terbium, used in energy efficient light bulbs, as well as the truly rare thulium, which has applications in x-ray devices."