Lodestone

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Lodestone

Lodestone or loadstone refers to naturally occurring pieces of intensely magnetic magnetite

Magnetite

Magnetite is a ferrimagnetism mineral with chemical formula Iron3Oxygen4, one of several iron oxides and a member of the spinel group....
that were used for magnetizing compass

Compass

A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's magnetic poles....
es.

Iron, steel and ordinary magnetite are attracted to a magnetic field

Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
, including the Earth's magnetic field

Earth's magnetic field

Earth's magnetic field is approximately a magnetic dipole, with one magnetic pole near the north pole and the other near the geographic south pole ....
. Only magnetite with a particular crystalline structure, lodestone, has the coercivity

Coercivity

In materials science, the coercivity, also called the coercive field, of a ferromagnet is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation ....
to act as a permanent magnet and attract and magnetize iron. The naturally occurring specimens are magnetized by the strong fields surrounding lightning

Lightning

File:Blesk.jpgLightning is an Earth's atmosphere discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcano or dust storms....
bolts.

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Encyclopedia

Lodestone or loadstone refers to naturally occurring pieces of intensely magnetic magnetite

Magnetite

Magnetite is a ferrimagnetism mineral with chemical formula Iron3Oxygen4, one of several iron oxides and a member of the spinel group....
that were used for magnetizing compass

Compass

Magnetic field

Earth's magnetic field

Coercivity

Lightning

Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets....
" comes from lodestones found in Magnesia

Magnesia

Magnesia , deriving from the tribe name Magnetes, is the name of the southeastern area of Thessaly in central Greece. The modern prefecture was created in 1947 out of the Larissa prefecture....
, a portion of ancient Thessaly, Greece.

In China, the earliest literary reference to magnetism lies in a 4th century BCE book called Book of the Devil Valley Master: "The lodestone makes iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
come or it attracts it." 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." By the 12th century the Chinese were known to use the lodestone compass for navigation. Also, Vikings used lodestone for navigation.

The lodestone has a hardness

Mohs scale of mineral hardness

Not to be confused with Siemens_#Mho, a unit of electric conductance.The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material....
of 5.5-6.5 and a black streak.

Lodestone

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