Rare earth elements and rare earth metals
are a collection of sixteen chemical elements in the
periodic table which naturally occur on the Earth. The
terms "rare earth" and "rare earth metal" are trivial
names that fall outside the official IUPAC nomenclature
system. Earth is an obsolete term for oxide; Rare was
used because some of these elements were believed to be
scarce in abundance as minerals. However, the term "rare
earth" is now deprecated by IUPAC, as these elements are
in fact relatively abundant in the Earth's crust.
