The Defense Department on Thursday became the largest shareholder in MP Materials, which owns the only rare earth mine in the U.S., amid a surge in demand for rare earths mined in the U.S. as China has curbed its rare earth exports amid a trade war with the U.S.

MP Materials Corp.’s stock skyrocketed in early trading Thursday, after the rare-earth producer said it inked a public-private partnership with the U.S. Defense Department to boost domestic magnet production and to reduce dependence on foreign sources.