Mullite

Mullite (3Al₂O₃·2SiO₂) is a synthetic or naturally occurring refractory mineral valued for its exceptional thermal stability, low thermal expansion, and creep resistance at elevated temperatures, making it indispensable in kiln furniture, advanced ceramics, and high-temperature insulation. Classified under a single US tariff line (2508600000), it is distinct from the precursor minerals (kyanite, andalusite) that convert to mullite upon firing. Canada and China are the leading suppliers to the US, with Germany and Hungary also among significant sources.