The Economist in 2019.
It is not that rare earth materials do not exist outside of China, although it sits on the largest quantity: approximately 30-40% of all known rare earth deposits. Rather, extracting the materials is a difficult and highly polluting process that China was willing to take on.... "making it practically impossible for competing companies outside China to get a foothold," according to the Danish Institute for International Studies.
China's de facto monopoly forms an acute problem: international reliance on them could hamper vital industries and national security at a time of maximum competition between China and the US.