Cobalt is a hard, brittle metal that occurs naturally in the environment and is a common by-product of nickel and copper mining activities. Cobalt can enter the environment from burning coal or oil, processing of cobalt-containing ores, and the production and use of cobaltcontaining chemicals. Cobalt is often mixed with metals such as iron or nickel to make alloys (mixture of metals). These alloys are used for parts in gas turbine aircraft engines; corrosion resistant alloys; high-speed, heavy-duty, high-temperature cutting tools and dies; and in magnets and magnetic recording media. It is also used as a chemical agent in the petroleum and chemical industries. Cobalt is commonly used in electroplating because of its appearance, hardness, and resistance to oxidation. Cobalt compounds have been used for centuries to create a rich blue color in glass, glazes, ceramics, porcelain, pottery, tiles, and enamels.Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth’s crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.