What is Magnetite?
Magnetite is one of the best minerals for showing that physical properties can be as memorable as colour. A sharp octahedron, a heavy black mass or a naturally magnetised specimen connects crystal chemistry with planetary magnetism and ore geology.
Mineralogy and crystal structure
Reference formula: Fe3O4. Magnetite is a cubic inverse-spinel iron oxide and one of the principal magnetic minerals in the Earth. Its strong response to a magnet, black streak and octahedral crystals help distinguish it from visually similar manganese and iron oxides. Magnetite is classified with oxides and has a cubic crystal system. Typical hardness is 5.5–6.5 on the Mohs scale and specific gravity is approximately 5.1–5.2.
Colour, lustre and habit
Typical colours include black, grey-black. The usual octahedral, cubic, massive habit and metallic, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Magnetite forms in or is associated with igneous rocks, metamorphic banded iron formations, skarns, hydrothermal deposits and placer concentrations. Important documented localities include Sweden, South Africa, the United States, Canada, Brazil, India and Australia.
The magnetic black classic
Magnetite is one of the best minerals for showing that physical properties can be as memorable as colour. A sharp octahedron, a heavy black mass or a naturally magnetised specimen connects crystal chemistry with planetary magnetism and ore geology.
Collecting and care
Protect polished faces from scratching and keep strongly magnetic specimens away from sensitive electronic or mechanical devices.
