Lodestone

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Lodestone or loadstone refers to naturally magnetized pieces of the mineral magnetite. They are naturally occurring magnets. Ancient people first discovered the property of magnetism through lodestone's attraction to iron.^[1] Pieces of lodestone, suspended so they could turn, were the first magnetic compasses,^[2][3][4][1] and their importance to navigation is indicated by the name lodestone, which in Middle English means 'course stone' or 'leading stone'.^[5] It is one of only two minerals that is found naturally magnetized; the other, pyrrhotite, is only weakly magnetic.^[6] Lodestone is black or brownish-black, has a hardness of 5.5-6.5 and a black streak.

Ordinary magnetite, like iron and steel, is attracted to a magnetic field, but does not tend to become magnetized itself. Only magnetite with a particular crystalline structure, lodestone, has the coercivity to be magnetized and become a permanent magnet. The naturally occurring specimens are magnetized by the strong fields surrounding lightning bolts.^[7]

One of the first references to lodestone's magnetic properties is by 5th century BCE Greek philosopher Thales of Miletus^[8] who is credited with discovering lodestone's attraction to iron and other lodestones.^[9] The name "magnet" may come from lodestones found in Magnesia, a portion of ancient Thessaly, Greece^[10]. In China, the earliest literary reference to magnetism lies in a 4th century BCE book called Book of the Devil Valley Master (鬼谷子): "The lodestone makes iron come or it attracts it."^[11] The earliest mention of the attraction of a needle appears in a work composed between 20 and 100 CE (Louen-heng): "A lodestone attracts a needle."^[11] By the 12th century the Chinese were known to use the lodestone compass for navigation.^{[citation needed]}

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