Definitions for: Lanthanum

[n] a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth

Webster (1913) Definition: Lan"tha*num, n. [NL., fr. Gr. ? to lie hid, to be
concealed.] (Chem.)
A rare element of the group of the earth metals, allied to
aluminium. It occurs in certain rare minerals, as cerite,
gadolinite, orthite, etc., and was so named from the
difficulty of separating it from cerium, didymium, and other
rare elements with which it is usually associated. Atomic
weight 138.5. Symbol La. [Formerly written also
lanthanium.]

Synonyms: atomic number 57, La

See Also: metal, metallic element

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