Lodestone
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Lodestone or loadstone refers to either:
- Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe3O4, one of several iron oxides.
- A piece of intensely magnetic magnetite that was used as an early form of magnetic compass.
Iron, steel and ordinary magnetite are attracted to a magnetic field, including the Earth's magnetic field. Only magnetite with a particular crystalline structure, lodestone, can act as a natural magnet and attract and magnetize iron. The direction pointing nature of lodestone was known as far back as 4th century China, where it was used in geomancy. By the 12th century the Chinese were known to use the lodestone compass for navigation, but far earlier magnetic bacteria (Italian) (http://it.wikipedia.org/wiki/Batteri_magnetotattici) had learned the trick. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field [1] (http://www.astronomycafe.net/qadir/ask/a11651.html).