Discovered in 1839 by C.G. Mosander in Stockholm, Sweden. Lanthanum is a soft, ductile, white metal which oxidises rapidly in air. It is one of the most reactive of the lanthanide group of elements, reacting with water to produce hydrogen gas. It has an abundance in the earth's crust of 32 ppm. At very low temperatures, lanthanum is super conducting (at 6K). It is used to manufacture special grades of optical glass which have specific refractive properties. Lanthanum can also be used in flints, and La³⁺ is used as a biological tracer for Ca²⁺. Radioactive isotopes of lanthanum have been tested for the treatment of cancer.