Cobalt is a grayish, hard, brittle metal closely resembling iron and nickel. These three metals are the only naturally magnetic elements on Earth. Cobalt exists in two allotropic forms that interconvert slowly. This property accounts for the fact that different physical properties may be reported for the element. Its atomic number is 27, its atomic weight 58.9332, and its chemical symbol, Co. It has a melting point of 2723 °F (1495 °C) and a boiling point of 5301 °F (2927 °C).

Cobalt was the first isolated in about 1735 by the Swedish chemist Georg Brandt (1694-1768). Brandt had studied medicine and chemistry at the University of Leyden and mining and metallurgy at Harz. He spent most of his life working for the Swedish government, first at the Bureau of Mines and later at the Royal Mint.

Brandt discovered cobalt while investigating a group of substances known as the "half-metals." By half-metal...