Magnetite gets its name from the fact that it attracts magnets. Some magnetite is called lodestone because it is a magnet itself, attracting iron particles. Notable deposits of magnetite can be found in Germany, Russia, South Africa and the U.S. Many properties, some that can be seen and some that cannot, are unique to magnetite.
Physical Characteristics
Magnetite is black and has a luster that can be either dull or metallic. Its fracture, or characteristic breakage under stress, can be subconchoidal, meaning the broken surface is flat but with irregular, rounded corners. It can also be completely uneven. There is no cleavage, meaning the individual crystals do not break and fragment smoothly. Magnetite can develop a yellowish-brown rust if left moist.
Crystal Structure and Chemical Formula
Magnetite is an iron oxide mineral. Its chemical formula is Fe2+Fe3+2O4. Impurities can take the place of either of the two Fe (iron). The crystals are usually octahedral in shape but can be dodecahedral as well as a combination of the two. They are, however, seldom cubic. They can appear as grains, veins or can be non-discernible, which is known as massive.
Magnetism
The magnetism of magnetite is caused by a transfer of electrons between the two Fe (iron) ions in the crystal structure. This exchange is called an electric vector and generates a magnetic field. Magnetite crystals can appear in igneous rock as it's forming. These crystals automatically orient with the polarity and direction of the Earth's magnetic field. Once the rock has formed and cooled, the position of the magnetite crystals is fixed. When looking at specimens from around the world, information can be gathered to understand continental movement throughout time.
Uses of Magnetite
Most magnetite is mined to extract the iron. This iron is in turn often used to make steel. In coal mining, high sulfur coal chunks are often floated across a mixture of powdered magnetite and a liquid in a process known as gravity separation. Pyrite, a sulfur-based mineral contaminate, sinks in the high-density slurry and the pure coal floats. Magnetite is also used as a toner in photography and as a nutrient in fertilizers.
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