Slate has its own distinct SITC classification reflecting its unique cleavage properties and end-use profile. Importers of slate curbstones, flagstones, or setts must classify those products under the appropriate slate heading rather than SITC 66131. The stone type should be clearly identified on all commercial documents, and a mineralogical description or supplier declaration may be requested by CBP to confirm the distinction.

The degree of surface finishing — rough-split, sawn, honed, or polished — can affect classification at the HTS level, as some tariff schedules distinguish between simply cut or sawn stone and further-worked or finished articles. Importers should ensure that the commercial invoice accurately describes the surface treatment and dimensional tolerances of the product, as these details determine the applicable HTS subheading and corresponding duty rate.