Cerium

A rare metallic element, occurring in the minerals cerite, allanite, monazite, etc. Symbol Ce. Atomic weight 141.5. It resembles iron in color and luster, but is soft, and both malleable and ductile. It tarnishes readily in the air.

a ductile grey metallic element of the lanthanide series; used in lighter flints; the most abundant of the rare-earth group