Magnetite and Lodestone

Magnetite and Lodestone are two varieties of the same material. Magnetite is a mineral commonly used as an Iron ore and is the most magnetic naturally occurring mineral.

Lodestone is a permanent magnet, but the majority of Magnetite is not. The leading theory currently is that this magnetism could be caused by lightning strikes.

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Appearance, Uses and History

Magnetite is one of the most important ores of Iron still used today – a banded sedimentary rock called taconite, a mixture of magnetite, hematite, and chert.

Magnetite is sometimes found in beach sand, in large quantities, where it is known as black sand.

Magnetite is extremely magnetic, attracted to a magnet. However, it is not a naturally occurring magnet. In certain areas, magnetite can affect navigation with a compass.

Lodestone is a naturally magnetic form of Magnetite, which acts as a magnet and does attract tiny particles of Iron. It is theorised that Lodestone is caused by lightning strikes to pieces of ground with high magnetite content near to the surface.

Historically, pieces of lodestone were used as a primitive form of compass. 

Magnetite forms part of the natural abrasive known as emery (a mixture of magnetite and corundum), although use of the natural emery has been superseded by a synthetic emery made by combining magnetite and aluminium oxide particles.

As an igneous rock forms, tiny crystals of magnetite may form inside. Due to their magnetism, they align themselves with the Earths magnetic field, which preserves the orientation of the Earths magnetic field at the moment of crystallisation. This means geologists are able to study the crystals and learn more about any changes to the magnetic field.

Locales

Magnetite is found worldwide, with significant deposits in numerous countries, most of which is not of any interest to mineral collectors due to its ‘massive’ nature.

Black sands can be found in Hong Kong, California, India, and New Zealand.

Large deposits of Magnesite can be found in Australia, Chile, Uruguay, Sweden, the USA, Mauritania, Romania, Norway, Ukraine and Peru.

For collectors, popular locales include

  • Valais in Switzerland
  • Nordmark in Sweden
  • Kola in Russia
  • Parachinar in Pakistan
  • Potosi in Bolivia
  • Several states of the USA, including Vermont, New York, New Jersey, and Pennsylvania.

Mineralogy

Chemistry
An Iron Oxide with the formula Fe3O4
Colours and Variations
Black to silver-grey.
Streak
Black
Luster
Metallic to submetallic
Fracture
Subconchoidal to uneven.
Transparency
Opaque
Crystal habit
Isometric, usually octahedral. Striations and layered growths are reasonably common. May also occur in grains, veins, rounded crystals, and as massive.
Mohs hardness
5 – 6.5
Specific Gravity
4.9 – 5.2
Fluorescence
N/A
Easiest testing method
Strongly magnetic, octahedral crystals, streak test.
Common Treatments
None.

Hazards and Warnings

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Arabic:

  • ماغنتيت

Hindi:

  • मैग्नेटाइट

Portuguese:

  • magnetita

Bengali:

  • ম্যাগনেটাইট

Indonesian:

  • magnetit

Punjabi:

English:

  • magnetite
  • lodestone

Italian:

Russian:

  • Магнетит

French:

  • Magnétite
  • Fer oxydé magnétique

Japanese:

  • 磁鉄鉱

Spanish:

  • Magnetita

German:

  • Magnetit

Korean:

  • 자철광

Thai:

  • แมกนีไทต์

Gujurati:

  • મેગ્નેટાઇટ

Mandarin and Traditional Chinese:

  • 磁鐵礦

Urdu:

  • میگنیٹائٹ

Further Reading / External Links