Cobalt is a ferromagnetic metal. Pure cobalt is not found in nature, but compounds of cobalt are common. Small amounts of it are found in most rocks, soil, plants, and animals.

The Curie temperature is 1115 °C, and the magnetic moment is 1.6–1.7 Bohr magnetons per atom. In nature, it is frequently associated with nickel, and both are characteristic minor components of meteoric iron. Mammals require small amounts of cobalt which is the basis of vitamin B12. Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer-treatment agent. Cobalt has a relative permeability two thirds that of iron. Metallic cobalt occurs as two crystallographic structures: hcp and fcc. The ideal transition temperature between hcp and fcc structures is 450 °C, but in practice, the energy difference is so small that random intergrowth of the two is common.

Name: Cobalt Symbol: Co Atomic number: 27 Atomic weight: 58.933195 (5) Standard state: solid at 298 K CAS Registry ID: 7440-48-4 Group in periodic table: 9 Group name: (none) Period in periodic table: 4 Block in periodic table: d-block Colour: lustrous, metallic, greyish tinge Classification: Metallic