Magnetite is an oxide of iron which occurs in igneous rocks, and in veins and replacement deposits; it is one of the most important ores of iron.

It usually occurs as a coarse, granular mass of black octahedral crystals, and produces a black streak.

Magnetite is permenantly magnetic, and was the first magnetic material to be discovered, known then as lodestone. A magnet will stick to magnetite, with some samples being sufficiently strongly magnetic to attract iron filings or, as shown here, staples.