Octahedral crystals of Magnetite, an iron oxide (Fe3O4) that is one part wustite (FeO) and one part haematite (Fe2O3). Magnetite, also known as loadstone, is naturally occurring and the strongest magnetic mineral on Earth. It is one of the three naturally occurring iron oxides, member of the spinel group of minerals. Its crystal symmetry is isometric, with crystals usually having an octahedral habitat. Black, brownish black metallic luster. Actual width of this sample is 150 mm