Yttrium and scandium are grouped with the rare-earth metals by chemical convention despite not being lanthanides. This heading specifically captures inorganic or organic compounds and mixtures of yttrium or scandium, distinguishing them from the broader lanthanide rare-earth compounds classified elsewhere. When a product is a mixed rare-earth compound containing yttrium alongside lanthanides, the predominant constituent and the specific chemical form determine the correct heading, and a binding ruling may be advisable for novel formulations.

Scandium is one of the scarcest commercially traded rare-earth elements, with primary production as a byproduct of titanium, uranium, and nickel refining rather than from dedicated mines. This byproduct dependency means supply is inelastic and can be disrupted by changes in the primary metal markets. The limited number of commercial-scale scandium oxide producers globally creates concentration risk, and long-term offtake agreements or strategic inventory are common risk-mitigation strategies for aerospace-grade aluminum alloy manufacturers.