Lodestone
From Wikipedia, the free encyclopedia
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.
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."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” Isis, Vol. 45, No. 2. (Jul., 1954), p.175</ref> 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."<ref>Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” Isis, Vol. 45, No. 2. (Jul., 1954), p.176</ref> By the 12th century the Chinese were known to use the lodestone compass for navigation.
Far earlier Magnetotactic bacteria had evolved to build miniature magnets inside themselves and use them to establish their orientation relative to the Earth's magnetic field [1].
