Before the development of appropriate grit synthesis methods, natural abrasives were used. Today, some natural materials are still used for polishing applications. The disadvantages of natural abrasives are their lower strength with the exception of natural diamond, as well as the non-reproducible grit quality [KLOC09, p. 17].
Quartz (silica, SiO2) includes the abrasives flint and tripolite with impurities of iron oxide (FeO) and titanium dioxide (TiO2) [KLOC09, p. 18]. Natural corundum has an Al2O3 content of 80-95 % [KLOC09, p. 18]. Emery consists of 37-70 % Al2O3 plus iron oxide Fe2O3, which can be considered as abrasive material itself [LEWI76, p. 8]. Garnet includes a group of minerals with similar crystal structure and is composed as X3Y2(SiO4)3. Most garnet grits for abrasive applications is from almandite (Fe3Al2(SiO4)3) [MENA00].
Boron carbide (B4C) is used as polishing, lapping, blasting, and grinding media for hard materials, in particular cemented carbide and fine ceramics [GREI06, KOMA97]. B4C is produced by different methods, such as carbothermic reduction of boric oxide B2O3 or magnesiothermic reduction of boric oxide B2O3 [GREI06].