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Rare earth elements (REEs) or rare earths are not rare in the sense of their abundance in the crust of the earth. These elements have earned this descriptive mostly because they are rarely concentrated enough for an easy recovery from their ores. The more abundant REE are each similar in crustal concentration to commonplace industrial metals such as chromium, nickel, copper, zinc, molybdenum, tin, tungsten, or lead (USGS Fact Sheet 087-02).

Even the two least abundant REE (Tm, Lu) are nearly 200 times more common than gold. At least one hundred minerals contain a RRE in their composition. However, only a few of these minerals have a significant percentage of RRE in their stoichiometry. The following list provides some noteworthy examples. The rare earth content of these minerals is expressed as the percentage of their weight in rare earth oxide (REO).

• Aeschynite, 36%

• Allanite, 30%

• Apatite, 19%

• Bastnäsite (one of a few rare earth carbonate minerals), 76%

• Britholite, 62%

• Brockite, 7%

• Cerite, 65%

• Cheralite, 5%

• Eudialyte (a fairly rare cyclosilicate mineral), 10%

• Fluocerite, 83%

• Gadolinite, 52%

• Loparite, 36%

• Monazite (an important source of thorium, lanthanum, and cerium), 71%

• Stillwellite, 60%

• Synchisite, 51%

• Wakefieldite, 35%

• Xenotime, 61%

• Zircon, 4%

• Zirconolite, 9%

The most abundant rare earth elements are found primarily in bastnaesite and monazite. Bastnaesite typically contains light rare earths and a small amount of the heavies, while monazite also contains mostly the light, but the fraction of the heavy rare earths is two to three times larger (Cindy Hurst). According to the U.S. Geological Survey, bastnaesite deposits in China and the U.S. make up the largest percentage of economic rare earth resources. Monazite deposits, found in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the U.S. make up the second largest segment.

Based on final 2008 reported data, the estimated 2008 distribution of rare earths by end use, in decreasing order, was as follows: metallurgical applications and alloys, 29%; electronics, 18%; chemical catalysts, 14%; rare-earth phosphors for computer monitors, lighting, radar, televisions, and x-ray-intensifying film, 12%; automotive catalytic converters, 9%; glass polishing and ceramics, 6%; permanent magnets, 5%; petroleum refining catalysts, 4%; and other, 3%. (Mineral Commodity Summaries 2010)

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