The Geology of Rare Earths: Not Rare, Just Never Concentrated
Rare earth elements are genuinely common in the crust. What is rare is finding them concentrated enough, and separated from each other, to be worth mining.
The name is genuinely misleading. Cerium, the most abundant of the 17 rare earth elements, is more common in the crust than copper. What is actually rare is finding them concentrated in one place and, just as importantly, finding them in a form where they can be separated from each other, since all 17 share such similar chemistry that they almost always occur mixed together.
Carbonatite and ion-adsorption deposits
The main commercial deposit types are carbonatite-hosted (associated with rare, carbonate-rich igneous rock, as at China’s Bayan Obo and California’s Mountain Pass) and ion-adsorption clay deposits, formed by the same kind of intense tropical weathering covered on cobalt’s and nickel’s geology pages, where rare earth ions bind loosely to clay minerals rather than forming a discrete mineral, China’s South China clay deposits being the classic example.
Why separation, not extraction, is the real geological challenge
Because all 17 elements share nearly identical chemical behaviour, a direct consequence of how their electron configurations fill, separating neodymium from praseodymium from the other 15 requires dozens of repeated solvent extraction cycles, a process chemistry problem as much as a mining one, covered in more depth on this material’s supply chain page.
Sources: deposit-type framing draws on standard economic geology references (USGS Mineral Commodity Summaries); production figures reference the production data elsewhere on this site.