What Are Rare Earth Elements?

Defining the Rare Earth Elements

Rare earth elements (REEs) are a set of 17 metallic elements that occupy a unique position on the periodic table. The group includes the 15 lanthanides — lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) — along with scandium (Sc) and yttrium (Y). Scandium and yttrium are included because they occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. Together, these 17 elements form the foundation of countless advanced technologies that define modern civilization.

Why Are They Called "Rare"?

The name "rare earth" is one of the most persistent misnomers in chemistry and geology. Most rare earth elements are not particularly rare in terms of crustal abundance. Cerium, the most abundant rare earth, is roughly as common as copper in the Earth's crust at approximately 60 parts per million. Even thulium and lutetium, the scarcest of the group, are more abundant than gold or platinum. The term "rare" dates back to the late eighteenth and early nineteenth centuries when these elements were first isolated from unusual minerals found in Scandinavian pegmatites. At the time, "earths" referred to metal oxides, and these particular oxides were considered rare because they were difficult to find in concentrated, economically extractable form.

The true scarcity of rare earths lies not in their crustal abundance but in their geochemistry. Rare earth elements are lithophile — they bond preferentially with oxygen — and they tend to be dispersed throughout common rock-forming minerals rather than concentrated in rich veins like copper or gold. Economically viable rare earth deposits require unusual geological conditions such as carbonatite intrusions, alkaline igneous complexes, or ion-adsorption clays formed through intense tropical weathering. This geological reality means that while rare earths are widespread, the number of deposits that can be profitably mined is relatively small.

The Complete List of 17 Rare Earth Elements

The 17 rare earth elements are conventionally divided into two subgroups based on atomic number and electron configuration:

For a detailed breakdown of each element with properties, uses, and supply data, see our complete rare earth elements list.

Unique Properties That Make Rare Earths Irreplaceable

What sets rare earth elements apart from other metals is their unique electronic structure. The lanthanides possess partially filled 4f electron orbitals that are shielded by outer 5s and 5p electrons. This shielding gives rise to extraordinary magnetic, optical, and catalytic properties. Neodymium and samarium produce the strongest permanent magnets known to science. Europium and terbium emit precise wavelengths of light that enable vivid display colors. Cerium's ability to rapidly cycle between oxidation states makes it an outstanding catalyst for automotive exhaust treatment and petroleum refining.

These properties are not simply superior versions of what other elements can do — they are qualitatively different. No known substitute can match the magnetic energy density of neodymium-iron-boron magnets. No alternative phosphor can replicate the narrow-band red emission of europium. This lack of substitutability is the core reason rare earths have become so strategically important. When a technology depends on a rare earth element, removing that element typically means redesigning the technology from the ground up, often at significant cost and performance penalty.

Discovery and Historical Context

The story of rare earth discovery spans more than two centuries. In 1787, Swedish army lieutenant Carl Axel Arrhenius found an unusual black mineral near the village of Ytterby outside Stockholm. This mineral, later named gadolinite, yielded the first rare earth oxide — yttria — when Finnish chemist Johan Gadolin analyzed it in 1794. Over the following 150 years, chemists painstakingly separated the remaining rare earths from one another, a process made exceptionally difficult by the near-identical chemical behavior of adjacent lanthanides. The final naturally occurring rare earth, lutetium, was not isolated until 1907, and promethium — the only radioactive lanthanide with no stable isotopes — was not confirmed until 1945 when it was produced in a nuclear reactor.

For most of the twentieth century, rare earths remained laboratory curiosities with limited industrial application. That changed dramatically in the 1960s and 1970s with the development of rare earth permanent magnets, first samarium-cobalt and then neodymium-iron-boron. The subsequent miniaturization of electronics, the growth of catalytic converter requirements, and the rise of fiber-optic communications created steadily growing demand. Today, rare earth elements are woven into the fabric of modern life in ways that most consumers never see.

Why Rare Earths Are Strategically Critical

Several converging factors elevate rare earths from merely useful to strategically critical. First, the concentration of mining and especially processing in China creates a single point of failure for global supply chains. China currently controls over 60 percent of mine production and more than 85 percent of rare earth separation and refining capacity. Second, the long lead times required to develop new mines — typically 10 to 15 years from discovery to production — mean that supply cannot respond quickly to demand shocks or geopolitical disruptions. Third, the accelerating deployment of electric vehicles, wind turbines, and advanced military systems is driving demand growth that significantly outpaces historical trends. The combination of concentrated supply, inelastic demand, and limited substitutability places rare earths at the top of virtually every critical minerals list published by governments worldwide.

Understanding rare earth elements requires going beyond the periodic table. It demands knowledge of geology, mineral processing, international trade, defense policy, and clean energy technology. The guides in this section aim to provide that comprehensive understanding. Continue exploring with our analysis of light versus heavy rare earths or learn about the crucial role of magnet rare earths in the energy transition.