magnetiet

Magnetiet, known in English as magnetite, is an iron oxide mineral with the chemical formula Fe3O4. It is the inverse spinel oxide that contains both Fe2+ and Fe3+ ions, and it has long been noted for its natural magnetic properties. The name derives from its magnetism, and historical references to lodestones reflect its role in navigation.

Physical properties include a black to steel-gray color, a metallic to submetallic luster, and a greenish-black streak. It has a Mohs hardness of 5.5–6.5 and a specific gravity around 5.15–5.20. Magnetiet is ferrimagnetic at room temperature, and its magnetic moment is strong enough to attract and retain magnetization; this property is responsible for its historical use in compasses and as a calibration material.

Natural occurrence: magnetiet occurs in a variety of geological environments, including igneous and metamorphic rocks, and is a common detrital mineral in sedimentary rocks. It is a major constituent of banded iron formations and forms through magmatic crystallization, metamorphic processes, and weathering of iron-bearing minerals. Magnetiet can oxidize over time to maghemite and, in oxygen-rich environments, to hematite.

Economic significance and uses: magnetiet is one of the principal iron ores alongside hematite. It is often processed by magnetic separation to produce concentrated ore for steel production. In modern technology, magnetiet particles are used in magnetic separation, catalysis, and some biomedical applications as magnetic nanoparticles.