Description
The mineral magnetite is an oxide of iron with valences of 2+ and 3+. Its chemical formula is Fe3+2Fe2+O4. Magnetite is a grayish-black, highly magnetic, naturally occurring mineral without cleavage, with an average density of 5.15. Its hardness is 5.5 to 6. The mineral is not radioactive. Its refractive index is 2.42, and the cubic mineral is isotropic. Gray and brown reflections can be observed with incident light. Ancient people discovered that magnetite crystals attract or repel each other depending on their orientation. This physical phenomenon is called magnetism. In China, the magnetic properties of magnetite were already being used as early as the 11th century BC. The terms "magnet," a medieval designation for a magnetic stone, and "magnetite," introduced by Wilhelm Haidinger in 1845, originated from the Latin root "magnet-" (with the nominative "magnes," magnet). Magnetic stones (Ancient Greek: λίθος μάγνης, lithos Magnes) were already known to the Greeks, according to the writings of Theophrastus. The Roman writer Pliny the Elder also mentions a stone called a "lodestone," which is said to have been named after Magnes, a Cretan shepherd who discovered the mineral on Mount Ida. He noticed that the nails in his shoes and the iron head of his staff were attracted to the rock containing the mineral. Pliny distinguished between several types of magnets, primarily between "male" and "female." Only the male magnet possessed the power to attract iron, and was therefore actually magnetite. Female magnets were probably manganese ore, which closely resembles magnetite, or a white mineral later called magnesite MgCO3. However, it is more likely that magnetite was named after Magnesia, a region in Thessaly, or after the city of Magnesia on the Meander, or also after other Greek or Asia Minor cities of the same name, where magnetic chunks of iron ore have been found for more than 2,500 years.
