Magnetite, also called lodestone, is an iron mineral made up of ferrous-deferric oxide (Fe3O4), and it owes its name to the Greek city of Magnesia. It has a strong magnetic quality due to a ferromagnetic phenomenon: the magnetic moments of different iron cations in the system are strongly coupled by antiferromagnetic interactions; this way, each cell (unit) has a non-compensated magnetic moment. The sum of these non-compensated magnetic moments, strongly coupled to one another, is responsible for the magnetic properties of magnetite.
Next to the hematite, the magnetite is one of the most important ores (minerals) due to its iron content (72%), which makes it the mineral with the highest iron content of all.
It is used as a high-density natural additive (from 4.65 kg/l to 4.80 kg/l)
on concrete used for radiology protection, exposed to marine conditions (docks, buildings, poles etc.), or vibratory
conditions (subway or train railroads).
It is also used an additive for asphaltic concrete in order to improve in-situ warming rates through microwaves. With the help of magnetite the adequate temperature (around 165 degrees C) can be reached in a very short time. Other iron oxides can fulfill the same purpose but a longer time of exposure to microwaves is required, which makes them unprofitable.
Magnetite is used in the production of brakes.
It is used specifically in coal washing using dense media. Magnetite increases the density of water, which facilitates the separation of coal from sterile material, thus reducing ash levels and incrementing BTUs (British Thermal Unit) in coal.
Magnetite is a very stable compound, even at high temperatures, though it can, at low temperatures and humid environments, slowly rust and form ferric oxide. Its stability at high temperatures allows it to act as a more than appropriate coating material for boiler tubes, which is why thermal treatments are carried out in industrial cauldrons, to form several layers of magnetite in its tubes.
Magnetite is used, grounded, on oil or petroleum spills to facilitate their recovery and clean aquatic surfaces with the use of electromagnets. It is also used in great quantities as a nutrient on oceanic surfaces for plankton, which provides the correct nourishment to the marine food chain from its base.