Edward G. Acheson invented the first synthetic abrasive in 1891. While searching for a way to make artificial diamonds, Acheson mixed clay and carbon, and then heated the mixture to create silicon-carbide crystals harder than all other substances except diamond. Since the early 1900s synthetic abrasives have been used more widely than natural abrasives. The synthetics can be produced cheaply and, if necessary, in large quantities. Among the most important are silicon carbide, aluminum oxide, and boron carbide. Silicon carbide, also called Carborundum, is widely used for making grinding wheels. Aluminum oxide, made from bauxite, is used for cutting hard metals. Boron carbide, a compound of boron and carbon, is one of the hardest abrasives. Carbide-coated products include saw blades and drill tips. Synthetic diamonds, first developed in 1955, are used in many types of drill bits and tool sharpeners. Synthetic Abrasives are however significant for shaping and cutting metals and other objects.