The rare earths are a group of 17 elements comprising Scandium, Yttrium, and the Lanthanides. The heavy rare earth elements, HREE. Light REE's are made up of the first seven elements of the lanthanide series - Lanthanum (La, atomic number 57), Cerium (Ce, atomic number 58), Praseodymium (Pr, atomic number 59), Neodymium (Nd, atomic number 60) Promethium (Pm, atomic number 61) and Samarium (Sm, atomic number 62).