Minerals containing cobalt were of value to the early civilizations of Egypt and Mesopotamia for colouring glass deep blue. Cobalt was announced to be an element by Georg Brandt about 1739 (or possibly 1735). He had been trying to demonstrate that the blue colour of glass was because of a new element, cobalt, rather than bismuth, an element often found in the same locations as cobalt. Cobalt was originally named from the German word "kobald" meaning "goblin" or evil spirit.

Cobalt salts in small amounts are essential to many life forms, including humans. It is at the core of a vitamin called vitamin-B₁₂. Grazing animals do not to do well in areas where there is little cobalt in the soil.

Cobalt is a brittle, hard, transition metal with magnetic properties similar to those of iron. Cobalt is present in meteorites. Ore deposits are found in Zaire, Morocco and Canada. Cobalt-60 (⁶⁰Co) is an artificially produced isotope used as a source of g rays (high energy radiation). Cobalt salts colour glass a beautiful deep blue colour.

Signs of deficiency: Anemia, anorexia, bleeding gums, confusion, dementia, depression, difficulty maintaining balance, headache, nausea, numb and tingling extremities, pale gums, pale lips, pale tongue, poor memory, retarded growth, shortness of breath, sore tongue, weakness in the arms and legs, weight loss, yellow eyes and skin. However, if a normal diet is followed a deficiency is most unlikely.

An excessively high intake of cobalt may damage the heart muscles, and may cause an over-production of red blood cells or damage to the thyroid gland.

Signs of toxicity : Cardiomyopathy, erythrocytosis, polycythemia, enlarged thyroid, diarrhea, fatigue, heart palpitations, numbness, and paleness. Some beers are cobalt-stabilized.

Since cobalt is part of the vitamin B12 molecule, the function of cobalt is interwoven with that of vitamin B12.