MP Materials’ goal to become a national rare-earths “champion” that can go toe-to-toe with China was turbocharged by Pentagon investment and an Apple deal. But its journey there highlights the hurdles American producers face.

MP Materials, which runs the only American rare earths mine, announced a new $500 million agreement with tech giant Apple on Tuesday to produce more of the powerful magnets used in iPhones as well as other high-tech products like electric vehicles.