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, silvery 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 for a long time thought to be due to the known metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue pigment-producing minerals; they were so named because they were poor in known metals and gave off poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.

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. The Copperbelt in the Democratic Republic of the Congo (DRC) and Zambia yields most of the global cobalt production. World production in 2016 was 116,000 tonnes (114,000 long tons; 128,000 short tons) (according to Natural Resources Canada), and the DRC alone accounted for more than 50%. 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(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color 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. Cobalt is also used in the petroleum industry as a catalyst when refining crude oil. This is to clean it of its sulfur content, which is very polluting when burned and causes acid rain. Cobalt is the active center of a group of coenzymes called cobalamins. Vitamin B12, the best-known example of the type, is an essential vitamin for all animals. Cobalt in inorganic form is also a micronutrient for bacteria, algae, and fungi.

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Atomic properties

Standard atomic weight58.9331 ±3·10-6
Atomic mass58.9331 u

Atomic radii

Radius (empirical)125 pm
Radius (calculated)152 pm
Covalent radius126 ±3 pm

Atomic shell

Electron configurationAr 3d7 4s2
Ionization energy(1st) 7.88101 eV
(2nd) 17.0844 eV
(3rd) 33.5 eV
(4th) 51.27 eV
(5th) 79.5 eV
Shell model

Physical properties

Density8.9 g·cm−3 (293.1 K)
Molar volume6.67·10-6 m3·mol−1
Speed of sound4,720 m·s−1


Melting point1,768 K
Boiling point3,200 K
Liquid range1,432 K


Melting enthalpy16.2 kJ·mol-1
Enthalpy of vaporization375 kJ·mol-1
Binding energy426 kJ·mol-1

Heat and conductivity

Specific heat capacity421 J·kg−1·K−1
Thermal conductivity100 W·m-1·K-1
Expansion coefficient1.3·10-5 K-1
Work function5 eV


Mohs hardness5
Brinell hardness700 NM·m-2
Vickers hardness1,043 NM·m-2

Elastic properties

Young’s modulus209 GPa
Shear modulus75 GPa
Bulk modulus180 GPa
Poisson’s ratio0.31

Electrical properties

Electrical conductivity1.67·107 S·m-1
Resistance5.999·10-8 Ωm



Optical properties

Reflectivity67 %

Chemical properties

Oxidation state2, 3
Standard potential-0.28 V (Co2+ + 2e- → Co)


Pauling scale1.88
Sanderson scale2.56
Allred-Rochow scale1.7
Ghosh-Gupta scale3.73 eV
Nagle scale1.44
Pearson absolute negativity4.3 eV

Other properties

Natural occurrenceprimordial
Crystal structureHexagonal close-packed
Goldschmidt Classificationsiderophile
Superconductorwithout transition tempperature
Price/kg32.8 USD

Natural abundances

3,000 ppb ≈ 3.01·1013 M☉
4,000 ppb ≈ 7.95·1012 Mt
600,000 ppb ≈ 600 g
Earth’s crust
30,000 ppb ≈ 831,000 Mt
0.08 ppb ≈ 109 kt
Flowing water
0.2 ppb ≈ 3.2 kt
Human body
20 ppb ≈ 1.4 mg