Heavy Rare Earth Elements (HREE)

Heavy rare earth elements (HREE) are the rare earths from gadolinium through lutetium, plus yttrium, under the split REEx uses. They are scarcer in the Earth's crust than the light rare earths, and two of them, dysprosium and terbium, keep the magnets in electric vehicle motors and wind generators working when they run hot. Most heavy rare earth ore has come from clay deposits in southern China and Myanmar. That makes this group the hardest part of the rare earth supply chain to rebuild elsewhere.

Which elements count as heavy rare earths

REEx files nine elements in the heavy group: gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium. The light rare earths run from lanthanum through europium, plus scandium. Yttrium is not a lanthanide, but it shares their chemistry and turns up in the same deposits, so it is counted as a rare earth (USGS Professional Paper 1802-O).

Not every source draws the line in the same place. USGS Professional Paper 1802-O (2017) puts lanthanum through gadolinium in the light group and terbium through lutetium in the heavy group. It adds yttrium to the heavy group because of its chemical and physical ties to those elements. The heavy rare earth chapter of the USGS Mineral Commodity Summaries 2026 also starts at terbium. It says yttrium is considered heavy but covers it in a separate chapter.

Gadolinium is the main border case. Some sources also use a middle group. A Holland & Knight summary described China's April 2025 export rule as covering "medium and heavy" rare earths. Lynas Rare Earths called samarium a heavy rare earth in its August 2026 annual results. REEx and USGS count samarium as light.

Why heavy rare earths are scarcer

Most rare earths are not as rare as the name suggests (USGS PP 1802-O). The heavy ones are less abundant than the light ones, according to the USGS. In USGS figures for average crustal abundance, thulium sits at 0.52 parts per million and terbium at 1.2, against 66.5 for cerium. Yttrium is the exception in the heavy group, at 33 parts per million (USGS PP 1802-O, Table O1).

The heavy rare earths are concentrated in one unusual deposit type, the ion-adsorption clay. These clays form in wet tropical regions. Groundwater leaches rare earths out of the granite, and they cling weakly to clay in the thick weathered soil above it. USGS PP 1802-O called the clays of southern China the world's primary source of heavy rare earths and noted that similar clay deposits elsewhere had not yet been brought into production on a significant scale.

Myanmar has since become the other major clay source. Global Witness reported in May 2024 that Myanmar had become the single largest source of heavy rare earths, with the material shipped to China for processing. Outside Asia, USGS reported that a mine in Brazil produced mixed ionic-clay concentrate with elevated terbium and dysprosium in 2025.

Why magnets depend on dysprosium and terbium

USGS PP 1802-O describes neodymium-iron-boron magnets as the strongest magnets known. They lose resistance to demagnetization as they heat up. Replacing a small share of the neodymium with dysprosium improves high-temperature performance, which matters in motors for hybrid cars and in wind turbines, according to USGS PP 1802-O.

Magnet makers have cut how much they use. In grain-boundary diffusion, a finished magnet is coated with dysprosium or terbium and heated. The heavy rare earth then collects along the boundaries between the magnet's grains, where it does the most to resist demagnetization. A 2021 review in Materials & Design calls the process the best route to higher coercivity with low heavy rare earth use. USGS says substitutes exist for some heavy rare earth uses but are generally less effective.

What the other heavy rare earths do

Most heavy rare earths have small, specialized markets. Their uses include refining catalysts, fiber optics, magnets, lasers and portable X-ray units, according to USGS.

• Gadolinium is the metal in gadolinium-based MRI contrast agents (DailyMed drug label).
• Erbium goes into the amplifiers that boost signals in long-distance fiber-optic cables (IEEE Spectrum, August 2026).
• Yttrium is used mainly in ceramics and phosphors, with smaller amounts in optical glass and laser crystals (USGS yttrium chapter).
• Holmium, thulium, ytterbium and lutetium serve specialist uses in lasers, medical equipment and scientific instruments.

China's hold on separation

The IEA reported in October 2025 that China accounted for about 91% of separation and refining of the magnet rare earths and 94% of sintered permanent magnet production. That figure covers neodymium, praseodymium, dysprosium and terbium only, not the rest of the heavy group.

From 2021 to 2024, all U.S. imports of terbium, holmium and lutetium compounds and metals came from China, and 86% of ytterbium imports did, according to USGS. Germany supplied about half of U.S. erbium imports, but USGS said that material was derived from concentrates and intermediates produced elsewhere. U.S. net import reliance for heavy rare earth compounds and metals was 100% in every year from 2021 through 2025.

Export controls on heavy rare earths

On April 4, 2025, China's Ministry of Commerce and customs agency placed seven rare earths under export licensing in Announcement No. 18. Five of them are in the REEx heavy group: gadolinium, terbium, dysprosium, lutetium and yttrium. The other two are samarium and scandium.

In October 2025, China moved to add holmium, erbium, thulium, ytterbium and europium to the list. It suspended that rule in November 2025, before it took effect (IEA; CIRS). Under Announcement No. 70, the suspension was set to end on November 10, 2026. As of early October 2026, China had not announced an extension of that suspension. The April controls had never been suspended and remained in force, according to Tech Times. USGS reported that China had begun issuing general export licenses to selected exporters by December 2025.

Separation outside China (as of October 2026)

A handful of projects aim to separate heavy rare earths outside China.

• Lynas Rare Earths, Malaysia. Lynas produced its first dysprosium oxide in May 2025 and its first terbium oxide in June 2025 at its Malaysian plant, according to the company's June 2025 ASX announcement. When it announced first dysprosium, Lynas called itself the only commercial producer of separated heavy rare earths outside China. It added samarium oxide, which REEx counts as a light rare earth, in March 2026, according to its March 2026 ASX announcement.
• MP Materials, Mountain Pass, California. The U.S. Department of Defense (now the Department of War) lent the company $150 million in August 2025 to build heavy rare earth separation (USGS). The company said the circuit reached mechanical completion in May 2026. In August 2026, it said it remained on track to begin producing dysprosium and terbium later in 2026, according to coverage of its earnings call. REEx found no public confirmation of heavy rare earth output as of October 2026.

Recycling

USGS reported that only small quantities of heavy rare earths were recovered from permanent magnets in 2025. In January 2025 the Pentagon awarded $5.1 million to a Houston recycler to recover rare earths from electronic waste (The Defense Post). In November 2025 the Pentagon offered a conditional $80 million loan to ReElement Technologies for a planned plant in Marion, Indiana. ReElement stopped pursuing the offer in July 2026 (NS Energy).

What drives heavy rare earth demand and supply

Demand for the group is led by dysprosium and terbium in magnets that must hold their strength at high temperature, chiefly in electric vehicle motors and wind generators. Supply depends on clay mining in southern China and Myanmar and on how China administers its export licenses. New separation plants outside China add supply only once they reach steady output.

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