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 stable cobalt isotope and the only isotope that exists naturally on Earth. Twenty-two radioisotopes have been characterized; the most stable, Co has a half-life of 5.2714 years, and Co has a half-life of 271.8 days, Co a half-life of 77.27 days, and Co a half-life of 70.86 days. All the other radioactive isotopes of cobalt have half-lives shorter than 18 hours, and in most cases shorter than 1 second. This element also has 4 meta states, all of which have half-lives shorter than 15 minutes. The isotopes of cobalt range in atomic weight from 50 u (Co) to 73 u