Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe3O4. It is one of the oxides of iron, and is ferromagnetic it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the naturally occurring minerals on Earth. Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. Small grains of magnetite are very common in igneous and metamorphic rocks.