Cobalt Cobalt Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in 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. 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 color was later thought by alchemists to be due to the known metal bismuth. Miners had long used the name "kobold ore" (German
Cobalt(III) hydroxide Cobalt(III) hydroxide Cobalt(III) hydroxide or cobaltic hydroxide is a chemical compound with formula or . It is an ionic compound, with trivalent cobalt cations and hydroxyl anions . The compound is known in two structurally different forms, "brownish-black" and "green". The brownish-black form is a stable solid and can be prepared by reaction of water solutions of cobalt(II) chloride and sodium hydroxide, followed by oxidation with ozone. The green form, formerly thought to be cobalt(II) peroxide, apparently requires carbon dioxide as a catalyst. It can be prepared by adding hydrogen peroxide to a solution of cobalt(II) chloride in 96% ethanol