Magnetite is a mineral, one of the two common naturally occurring oxides of Iron (chemical formula Fe3O4) and a member of the spinel group. Magnetite is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, and this was how ancient people first noticed the property of magnetism.
Small grains of magnetite occur in almost all igneous and metamorphic rocks. It is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and a black streak.
The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide.
Read more about Magnetite: Properties, Distribution of Deposits, Biological Occurrences, Synthetic Magnetite, Gallery of Magnetite Mineral Specimens