Magnetite

Magnetite is a mineral whose primary component is an iron oxide that contains equal amounts of iron(II) and iron(III). Its empirical formula is Fe₃O₄, and it is often expressed as iron(II,III) oxide. In the past, it has been called ferrous–ferric oxide and triiron tetraoxide.

Magnetite is found in igneous, metamorphic, and sedimentary rocks. As its name implies, it is magnetic; it and other inherently magnetic iron-containing minerals are described as being ferrimagnetic. Magnetite is in the hexoctahedral crystal class; in the 3-D crystal structure, the purple atoms are iron, and the red atoms are oxygen.

Magnetite’s greatest use is as an important iron ore for steel manufacture. Other applications are as a catalyst in the Haber process for making ammonia, as a pigment for paints and ceramics, and as magnetic micro- and nanoparticles for a variety of processes and materials.

Studying an intriguing application of magnetite in nature, Lewis C. Naisbett-Jones, David L. G. Noakes, and colleagues at the University of North Carolina (Chapel Hill), LGL Ecological Research Associates (Bryan, TX), Oregon State University (Corvallis), and the Oregon Hatchery Research Center (Alsea) discovered that salmon use tiny magnetite crystals in their tissues to help them make their way from far out in the ocean back to their inland spawning locations.

The researchers subjected juvenile chinook salmon to strong magnetic pulses to show that the fish oriented their movements according to the direction of the magnetic field. Their results led the researchers to conclude that salmon are guided by Earth’s magnetic field to return to the rivers where they spawned.