lanthanum

n. (La) rare metallic element (Chemistry)

Lanthanum (IPA: ) is a chemical element in the periodic table that has the symbol La and atomic number 57.
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Noun
1. a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth
(synonym) La, atomic number 57
(hypernym) metallic element, metal

(n.)
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.
  

Atomic Mass : 138.9055
Atomic Number : 57
Name Origins: From the Greek, lanthanein = "to lie hidden."
Year Discovered : 1839
Discovery Credits : Discovered by C. G. Mosander at Stockholm, Sweden.
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