Szumigala and Werdon reported in 2012 on rare-earth elements, their uses, and current worldwide sources of their production. A summary of some Alaska occurrences of rare-earth elements and associated rocks is also included. This information circular is meant to be non-technical. A brief bibliography of geology papers describing Alaska rare-earth-element occurrences is included for those interested in more detailed geological information on rare-earth-element deposits in Alaska.
Rare-earth elements and the supply of and demand for these resources are currently significant news items. The global mining industry has ramped up exploration for mineral deposits containing rare-earth elements to meet the perceived future demand. High prices for rare-earth elements continue to drive exploration. Rare-earth elements (REEs) are a group of chemical elements that occur together in the periodic table of the elements. The group consists of the 15 lanthanide elements: 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). Yttrium (Y) is generally included with the rare-earth elements because it is chemically similar to the lanthanide elements and it is generally found in minerals that also contain rare-earth elements. Scandium (Sc) also occurs in most rare-earth-element deposits and is sometimes classified as a rare-earth element. The rare-earth elements are all metals and the group is often referred to as the “rare-earth metals.” These metals have many similar properties, which often cause them to be found together in mineral deposits.
The rare-earth elements are often informally subdivided into “heavy rare earths” and “light rare earths” based on the atomic number of the element. Lanthanum, cerium, praseodymium, neodymium, promethium and samarium, with atomic numbers 57 through 62, are generally referred to as the “light rare earths.” Yttrium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, with atomic numbers 39 and 63 through 71, are generally considered the “heavy rare earths.” Although yttrium, with an atomic number of 39, is lighter than the light rare-earth elements, it is included in the heavy rare-earth group because of its chemical and physical associations with heavy rare earths in natural deposits.
REEs form iron gray to silvery lustrous metals that are typically soft, malleable, and ductile, and usually reactive, especially at elevated temperatures or when finely divided. Melting points for the REEs range from 798°C for cerium to 1,663°C for lutetium. The principal REE ores contain one or more of the following minerals or material: bastnäsite, allanite, loparite, monazite, and the lateritic ion-adsorption clays.
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