Unexpanded perlite and vermiculite are raw mineral feedstocks that have not yet undergone the high-temperature expansion process. Once expanded, they are classified as processed mineral products under different headings. Importers receiving material that has been partially or fully expanded at origin should verify the correct classification with a licensed customs broker, as the physical state at time of importation determines the applicable heading.

Certain vermiculite deposits — most notably the Libby, Montana source — were historically associated with naturally occurring asbestiform amphibole minerals. While that specific domestic source is no longer commercially active, importers sourcing vermiculite from any origin should request supplier documentation confirming the deposit has been tested and found free of asbestiform contamination, both for regulatory compliance and downstream customer requirements.