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metallic rare earth element, 1841, coined in Modern Latin by Swedish chemist and mineralogist Carl Gustav Mosander (1797-1858), who discovered it in 1839, from Greek lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). So called because the element was "concealed" in rare minerals.
lanthanum lan·tha·num (lān'thə-nəm)
A soft malleable metallic rare-earth element used in glass manufacture. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,455°C; specific gravity 6.145 (at 25°C); valence 3.
A soft, malleable, silvery-white metallic element of the lanthanide series. It is used to make glass for lenses and lights for movie and television studios. 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 Periodic Table.
(La), chemical element, rare-earth metal of transition Group IIIb of the periodic table, prototype of the lanthanoid series of elements. Lanthanum is a ductile and malleable, silvery-white metal, soft enough to be cut with a knife. The element was discovered as the oxide (lanthana) in 1839 by Carl Gustaf Mosander, who distinguished it from cerium oxide (ceria). Its name is derived from the Greek lanthanein, meaning "to be concealed," indicating that it is difficult to isolate