Lanthanum 's a chemical element with the symbol La and atomic number 57. Lanthanum's a silvery white metallic element that belongs to group 3 of the periodic table and's a lanthanoid. It's found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum's malleable, ductile, and soft enough to be cut with a knife. It's one of the most reactive of the rare-earth metals. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silico… (More on Lanthanum)