Lodestone

  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.

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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 name "magnet" comes from lodestones found in a place called Magnesia.

In China, the earliest literary reference to magnetism lies in a 4th century BC book called Book of the Devil Valley Master (鬼谷子): "The lodestone makes iron come or it attracts it."^[1] The earliest mention of the attraction of a needle appears in a work composed between 20 and 100 AD (Louen-heng): "A lodestone attracts a needle."^[1] By the 12th century the Chinese were known to use the lodestone compass for navigation.

For some fascinating history of lodestone, see Verschuur's book.^[2]

References

See also

• Magnetism
• Lode Star