A bright, soft, silvery, metallic element of the lanthanide series obtained commercially from the mineral monazite, having an x-ray emitting isotope that is used in portable medical x-ray units. Atomic number 69; atomic weight 168.934; melting point 1,545°C; boiling point 1,950°C; specific gravity 9.321 (at 25°C); valence 2, 3. See Periodic Table.