Rare earth elements are a set of seventeen elements which consists of fifteen lanthanide elements plus scandium and yttrium. These elements are: cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y). Scandium and yttrium are classified as rare earth elements because they are likely to occur in the same ore deposits as the lanthanides and display their chemical properties. Although they are called rare, they are abundant in the earth crust with cerium being the 25th most abundant element but they have a tendency to occur together in nature and are difficult to separate from one another.
