metal quality rare earth metal quality A metal quality of material that is rare on earth. As defined by the International Union of Pure and Applied Chemistry, a rare earth metal element is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Despite their name, rare-earth elements are – with the exception of the radioactive promethium – relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, more abundant than copper. However, because of their geochemical properties, rare-earth elements are typically dispersed and not often found concentrated in rare-earth minerals; as a result economically exploitable ore deposits are less common. Kaiyong Liu, Oliver He https://en.wikipedia.org/wiki/Rare-earth_element The first rare-earth mineral discovered (1787) was gadolinite, a mineral composed of cerium, yttrium, iron, silicon, and other elements. This mineral was extracted from a mine in the village of Ytterby in Sweden; four of the rare-earth elements bear names derived from this single location.