Rare Earths Are Not Rare

Cerium sits at about 60 parts per million in the Earth's crust, which makes it roughly the twenty-fifth most abundant element there is and puts it comfortably ahead of copper. Neodymium, lanthanum and yttrium are each more abundant than lead. Even thulium and lutetium, the scarcest members of the family that has a stable isotope at all, run around half a part per million — an order of magnitude more common than silver, which nobody describes as rare.

So the name is wrong twice over. They are not rare, and they are not earths.

Where a bad name comes from

"Earth" is eighteenth-century vocabulary. Before anyone knew what an element was, chemists classified as an earth any powdery oxide that resisted every attempt to break it down further: lime, alumina, magnesia. When a new one turned up that behaved like an earth and came from an unfamiliar mineral, it got filed the same way.

The unfamiliar mineral was a heavy black rock picked up in 1787 in a quarry at Ytterby, a village on an island outside Stockholm. That single quarry eventually yielded the first samples of an extraordinary number of elements, and four of them are named after the village directly: yttrium, terbium, erbium and ytterbium. No other place on Earth has four elements named after it.

"Rare" made sense in 1787 too, because the oxide was genuinely hard to come by and appeared to exist in tiny quantities. What nobody realised for another century was that they were not looking at one substance. They were looking at a mixture of about fifteen chemically near-identical elements that took the whole of the nineteenth century to prise apart, with each apparent discovery turning out to contain two more.

Why they refuse to separate

No other family in the table resists being taken apart the way the lanthanides do, and the reason lies one shell below the surface of the atom.

Across the series, the electrons being added go into the 4f subshell, which sits underneath the outer shells rather than outside them. From a chemical point of view the outside of the atom barely changes from one element to the next. Almost all of them form a 3+ ion, almost all of those ions are close to the same size, and their salts therefore have close to the same solubility, close to the same crystal habit and close to the same everything else. The ionic radius shrinks steadily across the row — the lanthanide contraction — but by such small increments that neighbouring elements differ by a per cent or two.

The consequence was one of the most tedious enterprises in the history of chemistry. Separation was done by fractional crystallisation: dissolve, crystallise, keep the fraction that is very slightly enriched, repeat. Charles James, working at the University of New Hampshire in the early 1900s, reportedly ran some 15,000 recrystallisations to obtain pure thulium compounds. That was normal practice, not an outlier.

Two elements escaped the tedium by having a second oxidation state. Cerium will go to 4+ and europium will go to 2+, and in both cases a change of charge changes the chemistry enough to allow a clean separation in a single step. They were the first to be isolated in quantity, and they are still the cheapest.

Practical separation of the rest arrived with ion-exchange chromatography, developed by Frank Spedding's group at Ames during the Manhattan Project for reasons that had nothing to do with magnets. Modern plants use solvent extraction instead, running the mixture through hundreds of mixer-settler stages in sequence, each one shifting the balance a fraction further. It works. It is also why a rare-earth refinery is a chemical plant the length of a football pitch rather than a smelter.

The real scarcity is in the processing, not the rock

Deposits are the second half of the story. Rare earths are abundant on average and almost never concentrated: they are scattered thinly through ordinary rock rather than gathered into veins the way copper and lead are. Economically workable ore comes from a small number of mineral types — bastnäsite and monazite chief among them — and most of those minerals carry thorium, which is radioactive.

That single fact reshaped the industry. Separating rare earths from monazite leaves behind low-level radioactive residue that has to be characterised, contained and licensed. Western processing largely shut down not because the geology ran out but because the regulatory and disposal burden made it unattractive, at precisely the moment a competitor was willing to carry it. China now mines somewhere around two-thirds of global supply and — the figure that actually matters — refines and separates roughly 90 per cent of it. A mine outside China has historically still had to ship its concentrate to China to be turned into anything useful.

That has begun to shift. Mountain Pass in California, which was the world's dominant producer before the 1990s, has been rebuilding domestic separation capacity, and Lynas became the first commercial producer of separated heavy rare-earth oxides outside China in 2025. Both are recent, partial and expensive.

Which ones the world is actually short of

Lumping all fifteen together disguises the real picture, because supply and demand are wildly uneven across the family.

• Cerium and lanthanum are effectively over-supplied. They dominate the ore, they are produced whether anyone wants them or not, and finding uses for them — catalytic converters, glass polishing, fluid catalytic cracking — is a persistent commercial problem rather than a constraint.
• Neodymium and praseodymium carry the magnet market, which is where most of the value now sits.
• Dysprosium and terbium are the genuinely tight ones. They occur in much smaller proportions in the ore, they concentrate in the geologically awkward heavy rare-earth deposits, and the applications that need them do not have a substitute.
• Promethium is the one honest exception to this entire article. It has no stable isotope, it decays away faster than geology can replenish it, and what exists worldwide at any instant is thought to amount to a few hundred grams. That element is rare.

And scandium, which most classifications count as a rare earth, is a different problem again: reasonably abundant, but so unwilling to concentrate into an ore of its own that almost the entire world supply arrives as a sideline from processing something else entirely.

What the name got wrong, and what is actually scarce

Rare earths got their name from a single Swedish quarry, at a time when "earth" meant an unbreakable oxide and when the fifteen elements in the sample looked like one substance. The abundance figures have contradicted the name for over a century.

What is genuinely scarce is the ability to separate them. Fifteen elements with nearly identical outer chemistry require hundreds of processing stages to pull apart, the ores that carry them usually carry thorium as well, and the countries that stopped doing that work did not stop because the rocks ran out. The bottleneck has always been downstream of the mine, and every supply crisis of the last fifteen years has been a refining crisis wearing a mining crisis costume.