No. The heading explicitly covers natural corundum and other natural abrasives whether or not heat-treated, so calcined or thermally processed natural corundum remains here. The key distinction is natural versus synthetic origin — synthetic abrasives such as fused alumina are classified in a different chapter.

Pumice is classified under subheading 251310 based on its identity as a natural volcanic glass with a characteristically porous, lightweight structure. It should not be confused with processed lightweight aggregates or expanded minerals, which may fall under headings covering construction materials.