Rare earths, on the other hand, have narrower supply chains and are often more difficult to extract, requiring more cumbersome processes to separate them from other minerals (as Lecoq de Boisbaudran learned). The United States has just one operational rare earth mine, in Mountain Pass, Calif., which produces around 15 percent of global rare earths.

A US producer of rare earth metals stopped shipments to China after Beijing placed export controls on similar materials crucial for defense and technology manufacturing.

MP Materials said on Thursday it had stopped shipping rare earth concentrate to China in response to the that nation's retaliatory tariffs and export controls following the levies imposed by U.S. President Donald Trump,