MP Materials, operator of the Mountain Pass mine in California’s Mojave Desert, is ramping up supplies of the critical ingredients and magnets as China tightens exports.

According to the Associated Press, America’s only rare earths mine is seeing a surge in interest after China imposed export controls in response to Trump’s tariffs. Mountain Pass Materials said it will halt exports to China and process only some of its mined material on-site while storing the rest.

China’s dominance of both mining and processing means these niche metals have become a cudgel to use against opponents.