Researchers have found a deposit of rare-earth minerals off the coast of Japan that could supply the world for centuries, according to a new study. The study, published in the journal Nature on Tuesday, says the deposit contains 16 million tons of the valuable metals. Rare-earth minerals are used in everything from smartphone batteries to electric vehicles. By definition, these minerals contain one or more of 17 metallic rare-earth elements (for those familiar with the periodic table, those are on the second row from the bottom).