Nickel is a hard, ductile and ferromagnetic metal that is highly polished and resistant to corrosion. Nickel is a ferrophilic element. The core is mainly composed of iron and nickel elements. In the crust, iron-mafic rocks contain more nickel than silico-alumina rocks. For example, peridotite contains 1,000 times more nickel than granite, and gabbro contains 80 times more nickel than granite.