China has tremendous power over the rare earths market. The country has the biggest mines, producing 270,000 metric tons (297,624 tons) of minerals last year compared to the 45,000 tons (40,823 metric tons) mined in the U.S. China supplies nearly 90% of the world’s rare earths because it also is home to most of the processing capacity.

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.

China is retaliating against U.S. tariffs by restricting exports of rare earth minerals. Minerals expert Gracelin Baskaran explains why these little-known-elements are so vital to defense and tech.