Samples of the different rare earth elements are measured before quality assurance testing at the Molycorp Minerals laboratory at the Mountain Pass Mine in Mountain Pass, California in this August 19, 2009 photo. The open-pit mine is home to the world's richest proven reserve of "rare earth" metals, a family of minerals vital to producing the powerful, lightweight magnets used in the engines of Toyota Motor Corp's Prius and generators in wind turbines. The same kind of magnets power the fins that steer precision-guided missiles. To match feature ENVIRONMENT-MINING/TOYOTA REUTERS/David Becker (UNITED STATES)