Lanthanum in an ampoule under argon, approx. 1cm. Image copyright: smart-elements.com.

Lanthanum (La) is a silver-white metallic element that is the prototype and second most abundant member of the lanthanide series. First identified by C. G. Mosander in Stockholm in 1839, its name comes from the Latin lanthana meaning 'to lie hidden.' Its chief ores are monazite and bastnaesite. Soft, malleable, and ductile, lanthanum is used as a catalyst in cracking crude oil, in alloys, and to manufacture optical glasses. Its most common isotope is 139La (99.91%).


atomic number 57
relative atomic mass 138.906
relative density 6.17
melting point 920°C (1,688°F)
boiling point 3,454°C (6,249°F)