Unroasted iron pyrites (FeS₂ in its natural mineral state) fall under SITC 27420. Once pyrites are roasted — thermally oxidized to drive off sulfur and produce iron oxide cinder — the product is classified under a different heading covering iron ores or residues. The roasting step fundamentally changes both the chemical composition and the commercial application of the material.

Unroasted pyrites retain commercial use in regions where they are a cost-competitive sulfur source for sulfuric acid plants, particularly where recovered petroleum sulfur is less accessible. They are also used in the production of sulfur dioxide, iron sulfate, and as a minor input in some pigment and chemical manufacturing processes. In most developed markets, however, recovered elemental sulfur has largely displaced pyrites as a sulfur feedstock.