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

Apple said on Tuesday it would invest $500 million into rare earths mine operator MP Materials, as the iPhone maker seeks to localize its mineral supply chain. The investment is part of a broader push to bring the production of its coveted iPhones to the United States and boost U.

The company has reportedly promised to commit $500 million in US rare earth supplies for iPhones, iPads, Macs — and everything else.