Rare earth elements are on everyone's lips, and for good reason: they are the silent foundation of much of modern technology , from electric motors and wind turbines to screens, fiber optics, and medical equipment. Despite their name, they are neither literally "earths" nor, with few exceptions, are they all that "rare." Even so, their extraction and refining are thorny issues, and this is where much of today's geopolitics is being decided.
Beyond the industrial debate, there's a global power struggle: China dominates production and, above all, refining , and every time it threatens to restrict exports, entire supply chains tremble. Meanwhile, Europe, Japan, South Korea, and the United States are seeking alternatives: new deposits, recycling, and more efficient design. Let's unravel, without mincing words, what these fuels are, how they were discovered, why they are so useful, where they are located, and what it means to depend on them.
What exactly are rare earth elements?
When we talk about rare earth elements, we are referring to 17 metallic chemical elements : the 15 lanthanides (from lanthanum to lutetium) plus scandium and yttrium, which are often found alongside them in the same deposits. Their name comes from the old custom of calling oxides "earths" and from how difficult it was to separate them in the 18th and 19th centuries; that's why the name stuck.
In reality, they are not extremely scarce in the Earth's crust ; cerium, for example, is as common as copper. The problem is not so much finding them, but rather that they appear very dispersed and mixed with other elements, which complicates and increases the cost of their separation. There is one notable exception: promethium (Pm) is radioactive and practically does not exist naturally; it is obtained in nuclear reactors from the fission of uranium.
From an astronomical perspective, their presence has a fascinating history: many of these elements are forged in extreme events such as neutron star mergers. Meteorites and enriched marine crusts help scientists reconstruct their origin and distribution in the Solar System, and even inspire strategies for their future exploration.
A laboratory story: from mystery to the periodic table
The saga begins in 1787, when Carl Axel Arrhenius discovered a very dense black mineral in Ytterby, Sweden . He suspected it held something new and named it "Ytterby heavy stone." In 1792, the Finnish chemist Johan Gadolin analyzed a sample: he found oxides of silicon, aluminum, and iron, and a significant fraction of an unknown oxide. That mineral, gadolinite, had the idealized formula Be₂FeY₂Si₂O₁₀ , and its study would lead to the discovery of yttrium (Y) and an entire family of elements.
Shortly afterward, Vauquelin and Klaproth confirmed the results and suggested the name "gadolinite" for the mineral and "yttrium" for the oxide of the new element, in reference to the site of the discovery. The connection had been for some time: as early as 1751, Cronstedt had described the "heavy stone of Bastnäs," which Berzelius and Hisinger studied in 1803 and from which they isolated ceria (CeO₂ ) and the element cerium (Ce), named after the planetoid Ceres.
The separations were laborious. In 1830, Carl Mosander isolated metallic cerium and discovered lanthanum (La) from ceria. He also identified a supposed "didymium" that decades later turned out to be a mixture of oxides: in 1885, Welsbach separated praseodymium (Pr) and neodymium (Nd). Mosander also detected two oxides in 1844 that he named erbium and terbium; their names were even used interchangeably in 1860, reflecting the chaos of the time.
At the end of the 19th century, the list grew steadily: Marignac obtained ytterbia ; Lars Nilson isolated scandium in 1879; Per Teodor Cleve identified holmia (Ho) and thulia (Tm) ; and Boisbaudran detected samarium in didymium, from which samarium (Sm) would later be isolated. In 1886, Boisbaudran himself obtained gadolinium (Gd₂O₃ ) and dysprosium (Dy) from "impure" fractions; europium (Eu, Demarçay, 1901) and lutetium ( Lu , Urbain, 1907) followed. Promethium was confirmed much later (Marinsky, Glendenin, and Coryell, 1944–1947) in fission byproducts in Tennessee.
Chemical and physical properties: what makes them unique
The lanthanides are electropositive metals that generally exist in the +3 oxidation state . Throughout the series, the so-called "lanthanide contraction" occurs: the ionic radii progressively decrease due to the increasing effective nuclear charge experienced by the 4f electrons. This detail, which is not insignificant, influences their chemistry and crystal structure.
Due to their ionic size, they form compounds with high coordination numbers and particular structural patterns. Their oxides, Ln₂O₃ , are polymorphic and adopt various structures (types A, B, and C). With halogens, they give rise to trihalides, LnX₃, throughout the series, with the exception that cerium also forms the tetrahalide CeX₄ with Ce⁴⁺.
Another striking family is the hydrides: all rare earth elements form fluorite-type hydrides , generally with an approximate stoichiometry of LnH₂ , although trihydrides and non-stoichiometric hydrides also exist. Binary nitrides, for their part, adopt the "rock salt" type structure, very simple but effective.
In magnetism and spectroscopy, their behavior is unique. The 4f electrons are the key players and are heavily shielded by the 5s² and 5p⁶ shells , so the chemical environment barely disturbs their energy levels. The spin-orbit coupling constants are large, so the ions typically have a single, well-defined ground state (with quantum number J), and the next excited state is sparsely populated at room temperature.
From this emerge their characteristic colors and f–f transitions , which are practically independent of the compound. To name a few: Pr³⁺ dyes green, Nd³⁺ dyes lilac, Sm³⁺ dyes yellow, Eu³⁺ dyes pale pink, while La³⁺ , Ce³⁺ , and Gd³⁺ are colorless. This "palette" is very useful, for example, in lasers and phosphors.
Minerals and types of deposits
Although more than 180 rare earth minerals have been described , only about 25 are of real economic interest. Among the most important are bastnaesite (a rare earth element fluorocarbonate), monazite (a phosphate), xenotime (a yttrium phosphate), loparite (a complex oxide rich in Ce, Na, Ca, Ti, and Nb), cerite (a silicate), and gadolinite (a silicate containing rare earth elements, beryllium, and iron).
The large deposits associated with these minerals are related to four main geological contexts. First, carbonatites , igneous rocks with more than 50% carbonates, such as Bayan Obo (China) or Mountain Pass (USA). Second, alkaline igneous rocks such as the nepheline syenites of Lovozero (Russia). Third, lateritic clays that form through in-situ alteration; southeastern China exploits more than 250 deposits of this type. Fourth, placer deposits where monazite is concentrated, such as the Matamulas deposit (Ciudad Real, Spain).
Furthermore, there is evidence of manganese-cobalt enrichment in ocean floor crusts, the exploitation of which is still being investigated. This is not science fiction: these are scenarios with real resources, although their economic and environmental viability is being closely scrutinized.
Production, reserves and refining: the power of the bottleneck
The figures vary depending on the source and the year, but the pattern remains the same: China clearly dominates the sector . Historically, annual production of rare earth oxides (REOs) has been around 160.000 tons, while in recent years it has reached hundreds of thousands of tons (for example, nearly 390.000 tons in some estimates). China provides the majority of the supply and easily exceeds 70% of the market; in refining, it accounts for approximately 90% of the capacity.
Among the pursuers are the United States as the second largest producer, Myanmar (often under the umbrella of Chinese companies), Australia , Thailand , and Nigeria . In terms of reserves, the USGS estimates around 90 million tons of REO equivalent globally: about half in China , some 21 Mt in Brazil, around 7 Mt in India, approximately 6 Mt in Australia, and about 4 Mt in Russia; other sources also detail very significant figures in Vietnam and Greenland , in addition to Norway with an identified deposit of ~1,57 Mt.
Europe is around 90% dependent on monazite, and its current production is minimal. Spain appears on the map with potential: in addition to the Matamulas placer deposit (Ciudad Real), there are expectations in Galicia, Castilla-La Mancha, Andalusia, and Extremadura. The Matamulas deposit has been estimated to contain around 29,9 million tons of monazite, and it has been suggested that it could contribute around 2.000 tons per year of REO (refined mineral oil), although all of this is contingent on technical, economic, and environmental viability.
Technological and everyday applications
Their list of uses is too long to fit in a tweet. To start with the most well-known, neodymium-iron-boron (Nd₂Fe₁₄B) permanent magnets have revolutionized electric motors, wind turbines, headphones, speakers, hard drives, and sensors. Dysprosium and terbium are added to improve their performance at high temperatures, especially in wind turbines and electric vehicles.
In optics and photonics, the lanthanides are unbeatable . Neodymium is the core of lasers such as YAG (yttrium aluminum garnet), YLF (yttrium lithium fluoride), and YVO4 ( yttrium vanadate), which emit in the infrared (around 1054–1064 nm) and are used in medicine and dentistry. Europium and terbium activate red, green, and blue phosphors for LED and fluorescent displays. Erbium enables amplification in optical fibers down to 1.55 μm for telecommunications.
Cerium, for its part, shines as a catalyst and polishing agent : it appears in self-cleaning furnaces, in the catalytic cracking of refining, and in the polishing of glass and optics. It is also part of alloys that "spark" in lighters (ferrocerium). Lanthanum raises the refractive index of optical glass and is used in lenses and as a component of Ni-MH batteries.
Yttrium (Y) is used in YAG lasers , phosphors in displays, high-temperature superconductors (YBCO) , stabilized zirconia (YSZ) for advanced ceramics, and yttrium iron garnet (YIG) in microwave filters. It also appears in coatings for energy-saving lamps and white LEDs, spark plugs, and as an additive in steels. Scandium (Sc) strengthens aluminum alloys in aerospace and enhances metal halide lamps.
In magnetostrictors, combinations such as terphenol-D (terbium + iron) and galphenol (gadolinium + iron) have applications in sonar, actuators, and robust sensors. In medicine, gadolinium is a contrast agent in magnetic resonance imaging , and holmium is used in surgical lasers. Thulium has been used in portable X-ray machines and compact lasers.
Medical imaging: phosphors and intensifying screens
Before the fully digital era, and even today in specific equipment, intensifying screens with rare-earth phosphors transform X-rays into visible light to reduce the dose to the patient. Their typical components include activators that determine the emitted color.
- Gd2O2S:Tb (terbium-activated gadolinium oxysulfide): emits green around 540 nm.
- La2O2S:Tb (larthanum oxysulfide activated with terbium): also green ~540 nm.
- Y2O2S:Tb (terbium-activated yttrium oxysulfide): emission in the blue (approx. 450–500 nm).
- LaOBr:Tm (thulium-activated lanthanum oxybromide): blue 450–500 nm.
- YTaO4:Tm (thulium-activated yttrium tantalate): blue-ultraviolet between 450–500 nm.
Compared to traditional calcium tungstate, these phosphors convert radiation more efficiently , allow for higher exposure speeds, and, with optimized technical parameters, reduce dose. The downside is that faster screens can increase quantum and radiographic noise; the balance between detail and dose is key.
Energy and green transition: three steps of impact
If we categorize its role in energy, three overlapping levels emerge . First, direct energy production: wind turbines use Nd-Fe-B magnets with approximately 30% neodymium in the magnetic fraction, and dysprosium and terbium additives for thermal stability. In the nuclear and space sectors, promethium-147 has been used in very low-power betavoltaic batteries for probes and potential military applications.
Second, energy efficiency: fluorescent and LED lighting with europium, terbium and yttrium phosphors; compact and high-performance electric motors thanks to neodymium and dysprosium magnets; and Ni-MH batteries whose cathodes are formulated with rare earth alloys with typical proportions of cerium (45–50%), lanthanum (25%), neodymium (15–20%) and praseodymium (5%).
Third, means that facilitate energy management: rare earth hydrides to store hydrogen in crystalline lattices and release it with slight heating; isotopes such as Sm, Gd, Dy, Ho and Er in reactor control; and a crucial role of La and Ce in catalytic converters of automobiles and in CeO2 type additives in fuels, which reduce the combustion temperature of soot and favor the cleaning of particulate filters.
In the market, beyond energy, approximately half of the production is consumed in magnets and catalysis . Magnets and luminescent materials stand out in terms of economic value. Consumption by element is highly skewed: neodymium (~49%) and praseodymium (~20%) dominate due to their use in magnets; followed by lanthanum (~6%), cerium (~4%), and terbium (~4%); the rest are below 2%. Terbium and lutetium are among the most expensive due to their relative scarcity and the difficulty of their separation.
Geopolitics, trade and recycling: the pieces on the board
In recent years, Beijing has announced strict export controls on both rare earth elements and extraction and processing technologies. With a near-monopoly—and controlling nearly 90% of refining—it can adjust the flow of these elements to suit its interests. This affects the United States, the European Union, Japan, and South Korea, all of which are heavily dependent on its Asian neighbor.
International summits have served as a stage for this tension: US and Chinese leaders have discussed the issue in Asia-Pacific forums , with negotiations aimed at postponing restrictions and buying time. Japan has sought strategic agreements to secure its supply chains, and South Korea is concerned about its dependence on automotive and electronics.
Ukraine has also been eyed for its subsoil resources, although its proven reserves of rare earth elements are not as abundant as previously suggested. Meanwhile, the military significance of these elements is readily apparent: an F-35 fighter jet incorporates more than 400 kg of rare earth elements, and a Virginia-class nuclear submarine can require more than 4.000 kg. All of this underscores their strategic importance.
Solutions? Several, but none quick fixes. Opening a deposit can take up to 30 years from discovery to production. The most sensible approach in the short and medium term is to promote recycling (urban mining): currently, it accounts for less than 1% of the total. Europe is moving in this direction, and Spain has put forward its Mineral Raw Materials Action Plan 2025–2029. Even so, mining projects will be needed, and above all, separation and refining capacity outside of China.
Myths and curiosities: neither "lands" nor so "rare"
The name is misleading. They are not "earths" in the colloquial sense, but metals whose oxides were discovered first. Nor are they so "rare" in abundance: cerium, for example, is among the 25 most common elements in the Earth's crust. What is rare—and radioactive—is promethium, which is practically absent in nature.
Its chemistry is captivating: the f–f transitions color ions and glasses , and its “immunity” to environmental changes makes the color of, for example, Eu 3+ or Nd 3+ highly reproducible regardless of the compound. This spectroscopic stability explains its success in lasers, phosphors, and calibration standards.
As a historical curiosity, Ytterby is the "little village of the four elements": yttrium, terbium, erbium, and ytterbium (and their echo in dozens of minerals and oxides). It is also paradoxical that names like holmium (for "Holmia," Stockholm) or lutetium (for Lutetia/Paris) remind us that science is often as much a human and geographical adventure as it is a chemical one.
To complete the technological circle, Nd-Fe-B magnets are cheaper and more powerful than samarium-cobalt magnets in many uses, and that's why they dominate in headphones, hard drives, and sensors; didymium (a mixture of Pr and Nd) colors glass and protects eyesight in welding goggles, and Nd-doped crystals are key players in modern photonics.
Viewed in perspective, this entire journey—from 18th-century mineralogy to 21st-century critical economics —shows why we depend so heavily on these discrete metals. Their combination of magnetic, optical, and catalytic properties has no easy substitute, and that's why their value chain, from mining to recycling, deserves such close attention.
The key idea to keep in mind is that the strategic value of rare earth elements lies not in their mere abundance , but in their geographic concentration, the control of refining, and the technical difficulty of separating them. Therefore, to strengthen resilience, we need both new, responsible projects, local processing capacity, increased recycling, and designs that use less material without sacrificing performance.