Unlike metals higher up on the table such as silver and gold, there's no good agent for dissolving elements so closely linked in atomic structure without destroying the target. It makes mining for them tedious and expensive.

"The reason they haven't been explored for in the U.S. was because as long as China was prepared to export enough rare earths to fill the demand, everything was fine â¿¿ like with the oil cartels. When China began to use them as a political tool, people began to see the vulnerability to the U.S. economy to having one source of rare earth elements," said Ian Ridley, director of the USGS Central Mineral and Environmental Resources Science Center in Colorado.

Two years ago, China raised prices â¿¿ in the case of Neodymium, used to make Prius electric motors stronger and lighter, from $15 a kilogram in 2009 to $500 in 2011, while Dysprosium oxide used in lasers and halide lamps went from $114 a kilogram in 2010 to $2,830 in 2011. It's also about the time China cut off supplies to Japan, maker of the Prius, in a dispute over international fishing territory.

That's when the U.S. government went into emergency mode and sent geologists to hunt for new domestic sources.

"What we have is a clash of supply and demand. It's a global problem. A growing middle class around the world means more and more people want things like cellphones," said Alex King, director of the Critical Materials Institute of the Department of Energy's Ames Research Lab in Iowa. "Our job is to solve the problem any way we can."

At the University of Nevada-Reno and the Colorado School of Mines, USGS scientists used lasers to examine extensive samples of rocks and ore collected across the West during the gold rush days by geologists from Stanford University and Cal Tech.

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