Few people had ever heard of the natural elements known as rare earth metals before a recent dispute between China and Japan. Yet these metals are used in devices like smartphones, flat screen televisions, hybrid car batteries, MP3 players and military equipment.In September, Japan detained a Chinese ship captain near disputed islands in the East China Sea. China denied that it stopped exports of rare earth metals to Japan to force his release. But the incident raised concerns. Japan is the world’s biggest importer of rare earth metals. And China produces ninety-seven percent of the world supply. China says it sold almost four billion dollars’ worth in two thousand eight. But marketing professor George Haley at the University of New Haven in Connecticut says China has always kept prices low.He says: “So unlike other minerals the price of rare earth elements has actually fallen.”Some countries with rare earth metals no longer mine them — including the United States. One reason is the low-cost imports from China. Another reason is concern about environmental damage. So what are these rare earth metals? Well, most of them are not rare; that is just their name. Several are more common than copper, lead or silver. People who remember the periodic table of the elements from chemistry class might recognize them. Rare earths include the fifteen lanthanide metals along with yttrium and scandium. Samuel Bader, a physicist at the Argonne National Laboratory near Chicago, says rare earths are often found together.But Mr. Bader explains that the same properties that make them hard to refine also make them valuable. He says: “Rare earth metals provide the world’s strongest commercial magnets. This is why they’re important. It’s that simple.”Rare earth magnets are lightweight and unaffected by conditions like high temperatures. So they work well in places like electric motors in hybrid vehicles or generators for wind turbines. Physicists use super-powerful magnets to speed particles and control radiation like X-rays. George Haley says they are found in electronics, fiber optics and other products. They are important not just for the economic success of the United States, but for defense and job creation at home.Next week, we’ll talk more about rare earth metals, and an American company that plans to start mining them again. For VOA Special English I’m Alex Villarreal.