Since the 1970s, man-made abrasives have been mass-produced, the most important of which are tantalum carbide and alumina. Carbide is commonly known as emery. Pure vermiculite is mixed with coke and added with a small amount of wood chips. It is placed in an electric furnace and calcined between 2,200 and 2,480°C for approximately 36 hours. Alumina, commonly known as corundum, is commonly used in industrial arc furnaces to heat and melt aluminum bauxite. Snow White is used as a heat sensitive metallic abrasive and Black is used for processing castings and steel. Synthetic diamond grinding wheels are the hardest and most necessary abrasives for sharpening carbide tools. Synthetic diamonds can also be made into tools of various shapes and sizes for cutting glass and ceramics. Boron carbide has a higher hardness than tantalum carbide and is not suitable for making grinding wheels. It can be used to replace expensive diamonds when polishing hard materials. Cubic boron carbide has twice the hardness of tantalum carbide and 2.5 times that of alumina, and is effective for grinding certain tool steels.