Flanked by hills and quarries in northeastern Jiangxi province, Jingdezhen is famed for its porcelain. The region’s rich deposits of kaolinite resulted in exceptional wares sought after by European colonial powers. Kaolinite is useful for another reason: it traps rare-earth elements, which are extracted today for many applications, from oil refining to making smartphones and missile-guidance systems. China supplies most of the United States’ rare-earths imports—an imbalance that has called attention amid the Sino-US trade dispute.