Magnetite: Mineral information, data and localities.
JacobsiteMagnetite Series. MagnesioferriteMagnetite Series. Magnetite is an important iron ore, along with hematite. Nanoinclusions of magnetite crystals cause the iridescence of Rainbow obsidian (Nadin, 2007). Extremely thin layers of 200nm octahedral crystals of magnetite give some basalt surfaces an iridescent sheen (Nadin, 2007).