Subheading 253010 covers perlite, vermiculite, and chlorites in their natural, unexpanded state — the raw mineral as mined or simply crushed. Once these minerals are heat-expanded (a process that dramatically increases their volume and changes their physical properties), they are classified under the chapter covering non-metallic mineral products, specifically in the heading for expanded minerals used as insulation or horticultural media.

Subheading 253020 is limited to naturally occurring magnesium sulfate minerals — kieserite as mined and natural Epsom salts. Chemically synthesized or refined magnesium sulfate is classified in the chapter covering inorganic chemicals. Importers should be prepared to provide documentation of natural mineral origin, such as a certificate of analysis indicating the mineral source, to support classification here.