"Rock Tumbler grit", also known as "rock polishing grit", can be a silicon carbide powder that is much harder than the types of rocks that are commonly polished in the rock tumbler. If it is tumbled within a barrel with rocks and water the abrasion caused through the grit particles https://raymondtpkfz.blogocial.com/a-secret-weapon-for-silicon-carbide-extrusion-64927338