USA Rare Earth will gamble most of its cash on one big acquisition.USA Rare Earth (USAR 2.17%) stock, one of a handful of start-up companies attempting to jump-start rare earth oxide mining and rare earth magnet manufacturing in the U.S., soared nearly 10% in early trading Monday before giving back all its gains.As of 1:25 p.m. ET, USA Rare Earth stock is basically flat -- even down a bit less than 0.1%. USA Rare Earth's big buyUSA Rare Earth announced it will buy British Less Common Metals, or LCM, in an e ...