Mineral Resource of the Month: Rare Earth Elements

August 27, 2021

by U.S. Geological Survey via EarthMagazine.org

The Sulfide Queen rare earth element mine in Mountain Pass, Calif. The U.S. has not mined rare earth minerals since 2002. Credit: Daniel J. Cordier

Daniel J. Cordier, rare earth commodity specialist for the U.S. Geological Survey, has prepared the following information on the rare earths, which have been used commercially since the 1880s.

The rare earths are a group of 17 metallic elements that occur in nature as nonmetallic compounds. Ironically, they’re not at all rare: As a group, they are about as abundant as lead in Earth’s crust. Rare earths earned their name to distinguish them from the alkaline earth elements (like beryllium, calcium and magnesium) that were found in the same deposits where rare earths were first discovered in Scandinavia in the late 1800s.

The rare earths include scandium, yttrium and the lanthanides. Most are classified into two groups: light rare earth elements (LREE) and heavy rare earth elements (HREE). The lighter group includes the lanthanide elements from atomic number 57 (lanthanum) through atomic number 64 (gadolinium), and the heavy group includes the lanthanide elements from atomic number 65 (terbium) through atomic number 71 (lutetium), along with yttrium. Scandium is not classified as either a light or a heavy rare earth element.

The similar atomic radii and oxidation states of the rare earth elements allow liberal substitution for one another within the crystal lattice sites of minerals, so all 17 typically occur in different percentages in each rare earth mineral. This substitution accounts for their wide dispersion in Earth’s crust and their characteristic occurrence within more than 100 minerals. However, their chemical similarity also makes it difficult and costly to separate them from each other in processing.

P: 845-346-1459 ext 100 
41 Dolson Avenue, Suite 4 | Middletown, NY 10940