Nickel. Bars of nickel, a metal used as an industrial catalyst and to add corrosion resistance and strength to steel. It is also used in alloys such as Invar and Mumetal. Nickel is found in the minerals pentlandite (nickel sulphide), pyrrhoite and garnierite. Nickel is also present in certain iron meteorites. Nickel is a malleable, ductile silvery transition metal. It is ferromagnetic below about 360 degrees centigrade. Although nickel-copper alloys have been known for several thousand years, nickel was not isolated until 1751 by Axel Friedric Cronstedt. Nickel has the chemical symbol Ni.