M7 boron carbide
Boron carbide - the hard granular material used for grinding and polishing of different surfaces (metal, wooden, etc. ), and also for sharpening and editing of tools. It cuts off and scratches out sharp sides of grains of camber of the processed surface, thereby leveling it.
Boron carbide, turns out alloyage of coke with boric acid. Artificial abrasive materials are applied more widely, than natural as they have high hardness and are homogeneous on structure and properties.