Rare earth is a term once used for a series of chemical elements now commonly known as the lanthanides. These elements are lanthanum, cerium, dysprosium, erbium, europium, gadolinium, holmium, lutetium, neodymium, praseodymium, promethium, samarium, terbium, thulium, and ytterbium. Scientists called them “rare earth” in part because they were assumed to be present in Earth’s crust only in tiny amounts. Later, scientists found some of them to be relatively abundant. For example, many of the rare earths are thousands of times more abundant in Earth’s crust than gold. For more information, see Lanthanide.
