Lanthanum metal is a white-silvery material at standard pressure and temperature. Lanthanum metal easily reacts with air forming a black patin surface. Lanthanum metal is the prototype for the lanthanides (elements from 58 to 71). Like these, it is silvery in color and quite soft. If counted among them, Lanthanum metal is the most reactive of those and the one with the highest atomic diameter. Lanthanum salts are used in optical lenses, alloys for special applications and in some batteries. In nature, Lanthanum always occurs in compounds.