Heavy Rare Earth Elements (HREE)

Heavy rare earth elements (HREE) are the higher-atomic-weight members of the lanthanide series — dysprosium, terbium, yttrium, gadolinium, erbium, holmium, thulium, ytterbium and lutetium. They are far scarcer than the light rare earths and considerably harder to separate.

The distinction matters commercially, not just chemically. Light rare earths are a hard problem; heavy rare earths are a crisis. China separates roughly 99% of the world's heavy rare earths, drawing on ionic clay deposits in southern China and Myanmar, and Western separation capacity outside that system is close to nonexistent.

HREEs carry the highest supply risk of any critical mineral group. Dysprosium and terbium make magnets survive heat, yttrium and europium make screens and turbine coatings work, and gadolinium makes MRI possible. For most of them there is no substitution path at scale.