Nickel is a hard, ductile, and ferromagnetic metal that can be highly polished and is corrosion-resistant. Nickel is an iron-loving element. The Earth's core is mainly composed of iron and nickel. In the Earth's crust, mafic rocks contain higher nickel content than felsic rocks; for example, olivine contains 1,000 times more nickel than granite, and gabbro contains 80 times more nickel than granite. Nickel is a silvery-white metal with magnetic properties and good plasticity. It has good corrosion resistance. Nickel is approximately silvery-white, hard, ductile, and ferromagnetic, capable of being highly polished and corrosion-resistant. When dissolved in nitric acid, it turns green. It is mainly used in alloys (such as nickel steel and nickel silver) and as a catalyst (such as Raney nickel, especially used as a hydrogenation catalyst).