Terbium

What Is Terbium

Terbium is element 65 — a heavy rare earth element sitting one position below dysprosium in the lanthanide series, with a function that is narrower, more specific, and more valuable per kilogram than almost any other rare earth in commercial use.

Its industrial purpose can be stated precisely. Terbium is added in very small quantities — typically 0.1–0.5% by weight — to NdFeB permanent magnets (neodymium-iron-boron — the strongest type of permanent magnet commercially available, used in EV traction motors, wind turbine generators, defense guidance systems, and industrial robotics) via a process called grain boundary diffusion, or GBD (a manufacturing technique that deposits terbium at the boundaries between individual magnetic grains rather than distributing it uniformly through the entire magnet, allowing the material to do its job with dramatically less of it — typically 30–50% less than older methods that blended terbium throughout). The effect of GBD is to raise the magnet's coercivity (resistance to demagnetisation — the property that keeps the magnet functioning under heat and mechanical stress rather than weakening over time) so that the magnet maintains full performance above approximately 80°C.

If that temperature threshold sounds modest, consider what sits above it. An EV traction motor under load regularly exceeds 100°C. A direct-drive wind turbine generator operates under sustained thermal stress. A defense actuator in a missile fin control system has no tolerance for magnetic degradation at any temperature. Without terbium or dysprosium in the magnet via GBD, these applications either fail or require a larger, heavier magnet that sacrifices the energy density that made NdFeB attractive in the first place.

The comparison to dysprosium matters here. Terbium and dysprosium are functional substitutes in GBD — both raise coercivity at operating temperature, both are added at the grain boundary level, and both address the same failure mode. But terbium is more effective per kilogram. The quantity required to achieve equivalent coercivity enhancement is smaller with terbium than with dysprosium. That efficiency premium is precisely why terbium commands a higher price than dysprosium — and why China's control of terbium supply is, if anything, more strategic than its control of dysprosium.

Why the Supply Picture Is More Constrained Than Neodymium or Dysprosium

Terbium is rarer than dysprosium. That sentence is worth sitting with. Dysprosium is already one of the least abundant commercially relevant rare earths. Terbium is less abundant still.

The geological reason is that terbium occurs in lower concentrations than dysprosium even within the ionic clay deposits (ore bodies in southern China where rare earth elements are loosely bound to clay particles rather than locked in hard rock, extractable by chemical leaching) that produce most of the world's heavy rare earths. When a tonne of ionic clay ore is processed, the terbium content is a fraction of the dysprosium content, which is itself a fraction of the neodymium content. The rare earths do not occur in equal proportion. Terbium is at the thin end.

The implications are compounding. Global terbium production runs at approximately 290 tonnes per year (IMARC Group, 2025) — a fraction of the roughly 2,000 tonnes per year for dysprosium, and a tiny fraction of the roughly 50,000 tonnes per year for neodymium. The addressable market is thin in a way that makes dysprosium look well-supplied by comparison.

China's dominance is near-total. Ionic clay deposits in Jiangxi, Fujian, Guangdong, and Yunnan provinces supply the overwhelming majority of global terbium. Myanmar's Kachin region adds supplementary heavy rare earth ore that flows to Chinese processors. Outside this system, there is no significant terbium supply. The Silverado Policy Accelerator data makes the result of China's April 2025 export license regime visible with precision: US terbium compound imports averaged 8.7 metric tonnes per month before the controls took effect. By April 2026, that figure had collapsed to 0.5 metric tonnes per month — a near-total cutoff. [Note: this figure carries a verification flag — verify directly at silverado.org before publish.]

0.5 tonnes per month is not a supply chain under pressure. It is a supply chain that has effectively stopped.

The Western policy response to terbium has been even thinner than its response to dysprosium — which was itself inadequate. There is no Western terbium producer at commercial scale. The projects that are working toward heavy rare earth production — Lynas's Fort Worth HREE facility, Energy Fuels' White Mesa Mill, NEO Performance Materials' Silmet plant — are targeting dysprosium and terbium together, but at sub-commercial quantities and timelines that extend well past the DFARS January 1, 2027 deadline.

The Silverado Data — 8.7 MT to 0.5 MT

The Silverado Policy Accelerator publishes monthly US import data for rare earth compounds. The terbium data is among the starkest in the dataset.

Before China's export license regime took effect — the April 2025 announcement that required government approval for every shipment of dysprosium, terbium, and other rare earth elements leaving China — US terbium compound imports averaged 8.7 metric tonnes per month. Not a large number in absolute terms. But for an application-critical material with no non-Chinese substitute and no domestic production, it was the entire supply.

By April 2026, that figure had fallen to 0.5 metric tonnes per month. The Silverado data — sourced from US Customs and Border Protection — does not distinguish between license denials and voluntary order cuts. What it shows is the result: the flow of terbium into the US market has collapsed to approximately 6% of its pre-control baseline.

The arithmetic does not work for any realistic estimate of what the defense supply chain alone requires — before civilian applications are counted at all. 0.5 metric tonnes per month is not a supply chain under pressure. It is a supply chain that has effectively stopped.

The 8.7 MT baseline was not sufficient to build a domestic magnet industry. The 0.5 MT current level is not sufficient to maintain one.

The DFARS Connection — January 1, 2027

DFARS 252.225-7052 (the Defense Federal Acquisition Regulation Supplement provision that requires the entire rare earth supply chain — mined, separated, processed, and melted — to be sourced from non-Chinese, non-Russian, non-Iranian, non-North Korean origins) takes effect January 1, 2027. The requirement applies to every magnet going into a US defense system from that date forward.

The terbium dependency sits at the center of what makes DFARS compliance structurally difficult in a way that discussions of neodymium compliance tend to obscure.

The path to a DFARS-compliant magnet runs as follows. A magnet manufacturer takes non-Chinese neodymium — sourced from MP Materials, Lynas, or another qualifying source — and combines it with iron and boron to produce a sintered NdFeB magnet. But for that magnet to perform at defense operating temperatures, it must undergo grain boundary diffusion with terbium or dysprosium. The GBD step is not optional for high-temperature applications. It is the step that makes the magnet suitable for defense use.

The terbium or dysprosium used in that GBD step must also be China-free under DFARS 252.225-7052. The requirement does not exempt the additives. The chain is the whole chain. A magnet manufactured in the United States from qualifying neodymium, using Chinese terbium in the GBD process, is not DFARS-compliant. The terbium is part of the chain. And there is effectively no non-Chinese terbium supply at scale.

This is not a theoretical gap in compliance planning. It is the gap. Neodymium supply chain development — the area that has received the most policy attention and investment — addresses one side of the magnet. GBD addresses the other. Without a qualifying terbium source, the magnet cannot be completed to defense standard.

The DFARS deadline is not moving. It was set by statute in the FY2023 National Defense Authorization Act and codified in the final rule published May 30, 2024. The GAO noted in its July 24, 2025 report on DoD supply chain visibility that DoD's tracking efforts provide “little visibility” into where goods are manufactured and that supply chain efforts are “uncoordinated and limited in scope.” CSIS warned in April 2026 that adhering to the DFARS requirement “may not be feasible” by the deadline. Neither assessment changes the deadline.

The MP vs USAR Lawsuit — Proof of Value

On May 22, 2026, MP Materials filed a lawsuit against USA Rare Earth in the Texas Business Court. The central allegation: that a former MP engineer, Kevin Elkins, took grain boundary diffusion technology — the proprietary process for applying terbium and dysprosium at magnet grain boundaries — to USA Rare Earth, which then disclosed it to FOM Technologies.

The lawsuit is instructive not for its legal merits — which remain to be determined — but for what it reveals about the value of the underlying technology.

Grain boundary diffusion is not a commodity manufacturing step. It is a precision engineering process that determines how much terbium or dysprosium a magnet requires. The better the GBD process, the less of the scarce heavy rare earth material the magnet needs. A manufacturer with superior GBD technology can produce a compliant, high-temperature magnet with less terbium input than a competitor using a less refined process. In a world where terbium supply has fallen to 0.5 metric tonnes per month in the US market, the ability to use less of it per magnet is not an incremental efficiency gain. It is a strategic capability.

Both MP Materials and USA Rare Earth are federally backed companies — receiving direct government investment, defense contracts, and policy support as part of the US domestic rare earth supply chain buildout. The fact that these two companies — partners in the same national security project, co-beneficiaries of the same policy framework — are fighting in court over the intellectual property to use less terbium is the clearest possible signal of how constrained the material is.

When the scarce resource is so scarce that two allied companies funded by the same government are litigating over the right to use less of it, the scarcity is not theoretical.

Why It Belongs on This List — The Physical Floor

The ScarceEarth framework for including a mineral in this intelligence set rests on one question: does this material sit at the physical floor of a system that cannot function without it?

Terbium sits at two simultaneously.

The first floor is the permanent magnet supply chain. Every high-performance NdFeB magnet that operates above 80°C — in an EV motor, a wind turbine generator, a defense actuator, a robotics system — requires terbium or dysprosium via grain boundary diffusion. There is no thermally stable high-performance magnet without it. The applications that need these magnets — electrification, renewable energy, defense modernization, autonomous systems — are not optional or cyclical. They are the structural demand of the next two decades of industrial and security infrastructure.

The second floor is DFARS compliance. The US defense supply chain cannot clear the January 1, 2027 statutory requirement without a DFARS-compliant terbium source. The requirement is not optional. The deadline is not flexible. The compliance path runs through a material of which there is effectively no non-Chinese supply. The physical floor is the regulatory floor. They are the same floor.

Terbium is not on this list because it is a speculative opportunity or an investment story. It is on this list because the systems that require it cannot function without it, the supply that exists is controlled by one country, and that country has already demonstrated the will to restrict it. The Silverado data — 8.7 MT to 0.5 MT in under a year — is not a price signal. It is a physical reality signal. The material stopped flowing. The applications that needed it are still running. The gap between those two facts is where the constraint lives.

The physical floor has its own physical floor. Terbium is one layer below the magnet. The magnet is one layer below the motor. The motor is one layer below the vehicle, the turbine, the weapons system. Every layer above depends on this one. The constraint at the bottom propagates upward through every system built on top of it.