Lanthanum was discovered in 1839 by a Swedish chemist named Carl Gustaf Mosander. He also discovered the elements erbium and terbium. The name lanthanum originates from the Greek word "lanthaneis," which means "to lie hidden."
Mosander was looking for impurities in cerium when he found lanthanum. Classified as a metal, lanthanum is part of the lanthanide group. This rare-earth metal has the atomic number 57 and the symbol La. It is used to make carbon arc lights, and a form of it is used in camera lenses. This silver-white element is soft and ductile. It is highly reactive for a rare-earth metal and oxidizes in the air quickly.