Strictly speaking, a rare earth is an oxide of a rare earth element. However, often rare earth elements themselves are loosely called "rare earths", and moreover the term is deprecated by IUPAC. The correct term for these used by many chemists is Rare terrestrials. An oxide is a chemical compound of oxygen with other chemical elements. ... Rare earth ore The rare earth elements are a relatively abundant group of 17 chemical elements (see Periodic Table) composed of scandium, yttrium, and the lanthanides. ... The chemical term earths was historically applied to certain chemical substances, once thought to be elements, and this name was borrowed from one of the four classical elements of Plato. ... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ...