Glossary

Magnetite is a naturally occurring iron oxide mineral with the chemical formula Fe₃O₄, and it is one of the most important and magnetic iron ores in the world. It contains both ferrous (Fe²⁺) and ferric (Fe³⁺) iron ions, making it a mixed-valence oxide and giving it unique magnetic properties. In fact, magnetite is the most magnetic naturally occurring mineral on Earth, a property that distinguishes it from other iron ores such as hematite.

In appearance, magnetite is usually black or dark gray with a metallic luster and a high density. When streaked on a surface, it leaves a black streak, unlike hematite, which leaves a reddish-brown one. Its natural magnetism can be strong enough to attract small iron objects or align itself with Earth’s magnetic field, which is why it was historically known as lodestone and used in some of the earliest magnetic compasses.

Geologically, magnetite forms in a wide range of environments. It can crystallize directly from igneous magma, occur as a product of metamorphism, or form through chemical precipitation in sedimentary rocks. It’s commonly found in banded iron formations (BIFs)—ancient layered sedimentary deposits that supplied much of the world’s iron ore. Large magnetite deposits are found in Australia, Brazil, Sweden, Russia, the United States, and South Africa, often mined alongside hematite.

From an industrial standpoint, magnetite is a major source of iron for steelmaking. The ore is typically concentrated using magnetic separation, since its magnetic properties allow it to be easily distinguished and isolated from surrounding rock. After concentration, it is smelted in a blast furnace, where carbon reduces the Fe₃O₄ to metallic iron. The reaction is: Fe₃O₄ + 4CO → 3Fe + 4CO₂

Magnetite is also used in other applications beyond steel production. Finely ground magnetite serves as a dense medium in coal washing, where it helps separate coal from impurities by density. It’s used in catalysts, recording tapes, pigments, water purification, and even in medical applications such as magnetic resonance imaging (MRI) contrast agents and targeted drug delivery systems.