Discovered in 1893 by Mosander, lanthanum is named from the Greek lanthanein, "to lie hidden". That is an apt description since lanthanum generally occurs along with other so-called rare earth elements and is very difficult to separate. The abundance of the metal is similar to that of zinc or nickel.
Lanthanum is used in the electrodes for high-intensity carbon-arc lamps and also in the production of high-purity europium metal (element 63). The pure metal is silvery white and malleable. It is soft enough to cut with a knife and will oxidize readily in the air as well as react with moisture. For that reason the metal is usually stored under oil or kerosene. Most lanthanum is extracted from monazite sands.
Stephen R. Marsden (ChemTopics)