Rare Earth Related Terms

Rare earth element ("REE") – A set of seventeen metallic elements with unique properties: chemical, catalytic, magnetic, metallurgical and phosphorescent.  While not particularly rare, their geochemical properties usually result in them being dispersed and not found in concentration significant enough to be recovered economically.  The elements include: Scandium (Sc), Yttrium (Y), Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb) and Lutetium (Lu).

Critical rare earth elements ("CREE) – In a study undertaken by the US Department of Energy, Critical Materials Study, December 2011, undertook a criticality assessment of rare earths evaluating two dimensions, importance to clean energy and supply risk.  They identified five rare earths as "critical" – Dy, Tb, Eu, Nd and Y – and two elements as "near-critical" – Ce and La. Rare Element includes Pr in its CREE list because of its ability to be substituted for Nd in high-intensity permanent magnets.

Bear Lodge REEs – Rare earth elements found at the Bear Lodge Project: Nd, Eu, Pr, Dy, Tb, Y, Ce, La, Sm and Gd.

Heavy rare earth elements ("HREE") – defined as the elements Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Yb.  Eu, Sm and Y are sometimes included because they behave like the other HREE.

Rare earth oxide ("REO") – the oxide form of rare earth elements

Total rare earth oxide ("TREO") – refers to the sum total of REO present in a deposit