The rare earth metals family is more formally known as the lanthanide series and that's because lanthanum kicks off that row of the table. Lanthanum is a relatively soft metal that when freshly cut looks has a medium gray luster similar to iron. However, if left out in the open its surface slowly oxidizes first turning dark then over time a puffy white that comes off at the touch. When stored in oil the oxidation still takes place and the luster is gone even faster but the reaction stops there and leaves the metal looking a blue-gray.

Comes both in oil as well as in glass ampules under argon to preserve its unoxidized state.

CAS 7439-91-0