MP Materials said on Thursday it had stopped shipping rare earth concentrate to China, in response to retaliatory tariffs and export controls, sending its shares down 6.3% in afternoon trading.

China seized mines and built factories. Japan took note and invested in Australia. But the United States did little despite concerns about control of supplies.

China has managed to hit the U.S. where it hurts the most in response to the Trump administration’s tariffs, with restrictions on global exports of certain rare-earth elements that the U.S. has little ability to produce or refine.