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.

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.