testo=<B>Cobalt</B><BR>Cobalt is a very hard, silvery-white, ferromagnetic metal. Although this material had been known for its compounds since ancient times, it was descovered between 1730-1734 by George Brandt. He showed that cobalt was the source that gave the blue colour to glass. Cobalt is not be found in a pure metallic form but only as mineral and it is a by-product of the extraction of copper or nickel.