Lanthanum

[Sarah]

A rare element of the group of the earth metals, allied toaluminium. It occurs in certain rare minerals, as cerite, gadolinite,orthite, etc., and was so named from the difficulty of separating itfrom cerium, didymium, and other rare elements with which it isusually associated. Atomic weight 138.5. Symbol La. [Formerly writtenalso lanthanium.]