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Magnetite

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Magnetite is rock mineral and one of the most important iron ore minerals with chemical formula is iron(II,III) oxide, Fe2+Fe3+2O4 .It also as the name magnetic minerals to attracted to a magnet. It is the most magnetic natural occuring minerals in the World. Small grains of magnetite occur in almost all igneous and metamorphic rocks.

Name: An ancient term, possibly an allusion to the locality, Magnesia, Greece.

Cell Data: Space Group: Fd3m (synthetic). a == 8.3970(1) Z == 8

Polymorphism & Series: Forms two series, with jacobsite, and with magnesioferrite.

Mineral Group: Spinel group.

Association: Chromite, ilmenite, ulvospinel, rutile, apatite, silicates (igneous); pyrrhotite, pyrite, chalcopyrite, pentlandite, sphalerite, hematite, silicates (hydrothermal, metamorphic); hematite, quartz (sedimentary).

Crystallography. Isometric; hexoctahcdral. Frequently in crystals of octahedral habit, occasionally twinned. More rarely in dodecahedrons. Dodecahedrons may be striated parallel to the intersection with the octahedrons. Other forms rare. Usually granular massive, coarse or fine grained.

Composition: Fe3 0 4 or FeFe20 4. Fe = 72.4 percent, 0 = 27.6 percent

Diagnostic Features: Characterized chiefly by its strong magnetism, its black color, and its hardness (6). Can be distinguished from magnetic franklinite by streak.

Chemical Properties of Magnetite

Chemical Classification Oxide minerals
Chemical Composition iron(II,III) oxide, Fe2+Fe3+2O4

Physical Properties of Magnetite

Color Black, gray with brownish tint in reflected sun
Streak Black
Luster Metallic
Diaphaneity Opaque
Mohs Hardness 5.5–6.5
Specific Gravity 5.17–5.18
Diagnostic Properties Dissolves slowly in hydrochloric acid
Crystal System Isometric

Optical Properties of Magnetite

Type Isotropic
RI values n = 2.42
Twinning as both twin and composition plane, the spinel law, as contact twins
Birefringence Isotropic minerals have no birefringence
Relief Very High
Colour in reflected light Grey with brownish tint

Occurence

Magnetite is a common ore of iron. It is found disseminated as an accessory mineral through most igneous rocks. In certain types through magmatic segregation becomes one of the chief constituents, and may thus form large ore bodies. Such bodies are often highly titaniferous. Most commonly associated with crystalline metamorphic rocks, also frequently in rocks that are rich in ferromagnesian minerals, such as diorite, gabbro, peridotite. Occurs also in immense beds and lenses, inclosed in old metamorphic rocks. Found in the black sands of the seashore. Occurs as thin plates and dendritic growths between plates of mica. Often intimately associated with corundum, forming the material known as emery.

The largest magnetite deposits in the world are in northern Sweden at Kiruna and Gellivare, and are believed to have formed by magmatic segregation. Other important foreign deposits are in Norway, Rumania, Ural Mountains. The most powerful natural magnets are found in Siberia, the Harz Mountains, on the Island of Elba, and in the Bushveld complex, Transvaal.

Uses of Magnetite

  • Most of the iron ore mined today is a banded sedimentary rock known as taconite that contains a mixture of magnetite, hematite, and chert. Once considered a waste material, taconite became an important ore after higher grade deposits were depleted. Today’s commercial taconites contain 25 to 30% iron by weight.
  • The abrasive known as “emery” is a natural mixture of magnetite and corundum. Some synthetic emery is produced by mixing magnetite with aluminum oxide particles.

Distribution

Many localities, even for fine crystals.

  • In Sweden, at Falun, Kiruna, Vastanfors, and elsewhere.
  • At Arendal, Norway.
  • From Zlatoust and Magnetigorsk, Ural Mountains, Russia.
  • In the Zillertal, Tirol, Austria.
  • From Traversella, Piedmont, Italy. In Switzerland, at Binntal and Rimpfischwang, Valais, and elsewhere.
  • In the Gardiner complex, beyond the head of Kangerdlugssuaq Fjord, Greenland.
  • From Bancroft, Ontario, Canada.
  • In the USA, around Lake Sanford, Essex Co., and in the Tilly Foster mine, Brewster, Putnam Co., New York; at Magnet Cove, Hot Springs Co., Arkansas; in the Iron Springs district, Iron Co., Utah. From the Cerro del Mercado, Durango, Mexico.
  • At Itabira, Minas Gerais, Brazil.

References

  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
Cite this article as: Geology Science. (2019). Magnetite. [online] Available at: http://geologyscience.com/minerals/magnetite/ [12th November 2019 ]
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