Lanthanum, a silvery white soft metal is one of the most reactive rare earth elements. When exposed to air, Lanthanum oxidizes quickly. It has a wide variety of uses in many commercial applications. It is used in carbon lighting, camera and telescope lenses, electron microscopes, cast iron, and lighter flints. Lanthanum has biological and chemical applications as well, serving as a catalyst in petroleum cracking and as a phosphate binder in the treatment of hyperphosphatemia.