Abrasives are sharp, hard materials that are used to grind the surface of softer materials. There are two categories of abrasives: natural abrasives and artificial abrasives. According to the hardness, there are two categories: superhard abrasives and ordinary abrasives. There is a wide range of abrasives, from softer household detergents, gemstone abrasives to the hardest material, diamond. Abrasives are essential materials for the manufacture of every precision product. Many natural abrasives have been replaced by artificial abrasives. With the exception of diamond, the properties of natural abrasives are not very stable, but they still have their use value. Diamond is the hardest abrasive, mainly in South Africa, which accounts for 95% of the world's total production, followed by Brazil, Australia, Guyana and Venezuela. Industrial diamonds range from gray-white to black, and can be crushed to make grinding wheels, abrasive belts, polishing wheels and grinding powders.