Cobalt is a chemical element with the symbol Co and atomic number 27. Like Nickel, Cobalt is found in the Earth’s crust only in chemically combined forms, 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. Cobalt-based blue pigments (Cobalt blue) have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the colour was later thought to be due to the known metal Bismuth. Today, some Cobalt is produced specifically from one of a number of metallic-lustered ores, such as Cobaltite (CoAsS). The element is, however, more usually produced as a by-product of Copper and Nickel mining.
Cobalt is primarily used in Lithium-ion batteries, and in the manufacture of magnetic, wear-resistant and high-strength alloys. The compounds Cobalt Silicate and Cobalt Aluminate (CoAl2O4, Cobalt blue) give a distinctive deep blue colour to glass, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, Cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high-energy gamma rays.