MAGNETITE: A NATURAL HISTORY
Not all magnetite can become lodestone. In order to magnetize, it must have a specific composition and structure. Unlike normal magnetite, lodestone contains traces of maghemite (cubic iron oxide, Fe2O3, a hematite polymorph) and ions of titanium, aluminum, and manganese. These impurities create an inhomogeneous structure that increases lodestone’s magnetic force and makes it a permanent magnet.
The Earth’s magnetic field is not strong enough to magnetize magnetite; the leading theory of how lodestone becomes magnetized focuses on lightning strikes. Lightning is an instantaneous and massive discharge of electrons that generates a very brief, but extraordinarily intense, local magnetic field. Upon striking a magnetite deposit, lightning’s magnetic field forces magnetite’s iron ions into more perfect alignment to increase its magnetism. Lodestone’s occurrence at or near the surface and not at depth supports the theory of lightning as the origin of its magnetism.
Two criteria distinguish lodestone from normal magnetite. Unlike normal magnetite, lodestone attracts and holds bits of steel, and it exhibits a distinct polarity that is detectable with a compass.
ANCIENT AGE AWARENESS
Awareness of lodestone’s magnetism seems to have evolved independently in Greece, China, and Mesoamerica. The Roman scholar and naturalist Pliny the Elder attributed the discovery of magnetism to Magnes, a shepherd in Magnesia, Asia Minor (now western Turkey). Magnes, who preceded Pliny by several centuries and was likely a mythical figure, supposedly discovered magnetism when lodestone attracted the iron nails of his shoes. Historians place the greater significance of Pliny’s writing in the fact that Magnesia became the etymological base of the