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.

Rare-earth miner MP MaterialsMP soared during stock market trade on Thursday after announcing a multibillion dollar public-private partnership with the U.S. Department of Defense to "dramatically accelerate the build-out of an end-to-end U.

Shares of the mining company soared 50% in early trading at $45.10, while the S&P 500 and Dow Jones Industrial Average were flat and down 0.2%, respectively. The agreements includ