Just because a company has "rare earth" in its name doesn't mean it's a viable rare-earths company.Rare-earth miner MP Materials said this morning the U.S. Department of Defense is making a big investment in its rare-earth magnets business, sending its stock price up 60% in morning trading. Now, investors in another rare-earths start-up, USA Rare Earth (USAR 14.10%), are wondering if their company might be next in line.It's pure speculation at this point, but still good enough for a 15.9% increase in share ...