Via geology.com from Forbes:

…  a Denver mining company called Molycorp (MCP), which is now spending nearly $1 billion to restart rare-earth-mineral production at Mountain Pass Summit and in the process revive a moribund U.S. industry. It won’t be easy. A decade ago the U.S. was the world’s biggest supplier of lanthanides, scandium, and other rare earths, and the Mountain Pass mine was the world’s largest producer of the minerals. Rare-earth elements enable the creation of super-magnets, which operate at high temperatures and are also used for a range of high-tech applications, from missile-guidance systems to compact fluorescent light bulbs to wind power turbines to motors in electric vehicles. Ironically, rare-earth minerals aren’t really rare; they get their name because they are spread widely throughout the earth’s crust in small concentrations that in most cases can’t be mined economically. In all, there are 17 rare-earth elements, which are typically found in varying proportions in the same ore deposits. China, with the world’s largest supply, has been ramping up production over the past two decades, leading to steep price drops that eventually forced the Mountain Pass mine to shut down operations in 2002. China now controls 97% of the market….