Chromite
General
Category	Mineral
Chemical formula	iron magnesium chromium oxide: (Fe, Mg)Cr2O4
Identification
Color	Black to brownish black
Crystal habit	Octahedral rare; massive to granular
Crystal system	Isometric; hexoctahedral
Cleavage	absent
Fracture	Conchoidal
Mohs scale hardness	5.5
Luster	Submetallic
Streak	Dark brown
Specific gravity	4.5 - 4.8
Refractive index	Subtranslucent to opaque
Fusibility	Infusible
Other characteristics	Weakly magnetic
Major varieties

Chromite is iron magnesium chromium oxide: (Fe, Mg)Cr₂O₄. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts; also, aluminium and ferric iron commonly substitute for chromium.

Contents 1 Occurrence 2 Uses 3 Mining 3.1 Minor production 4 References 5 External links

[edit] Occurrence

Chromite is found in peridotite from the Earth's mantle. It also occurs in layered ultramafic intrusive rocks.^[1] In addition, it is found in metamorphic rocks such as some serpentinites. Ore deposits of chromite form as early magmatic differentiates. It is commonly associated with olivine, magnetite, serpentine, and corundum. The vast Bushveld igneous complex of South Africa is a large layered mafic to ultramafic igneous body with some layers consisting of 90% chromite making the rare rock type, chromitite.

[edit] Uses

Chromite is also used as a refractory material, because it has a high heat stability.^[2]

The only ore of chromium is the mineral chromite. The two main products of chromite refining are ferrochromium and metallic chromium, for those products the ore smelter process differs considerably. For the production of ferrochromium the chromite ore (FeCr₂O₄) is reduced with either aluminium or silicon in a aluminothermic reaction and for the production of pure chromium the iron has to be separated from the chromium in a two step roasting and leaching process.^[3]

[edit] Mining

In 2002 14,600,000 metric tons of chromite have been mined. The largest producers have been South Africa (44%) India (18%), Kazakhstan (16%) Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world production. ^[4][5]

[edit] Minor production

In Pakistan, Chromite is mined from the ultramafic rocks in mainly the Muslim Bagh area of Zhob District of Balochistan. Most of the chromite is of metallurgical grade with Cr₂O₃ averaging 40% and a chrome to iron ratio of 2.6:1. Afghanistan has significant deposits of high grade Chromite ore.

Recently, the biggest user of Chromite ore has been China, importing large quantities from South Africa, Pakistan and other countries. The concentrate is used to make ferrochromium, which is in turn used to make stainless steel and some others alloys.

[edit] References

• Dana's Manual of Mineralogy ISBN 0-471-03288-3
• Guilbert, John M., and Park, Charles F., Jr. (1986) The Geology of Ore Deposits, Freeman, ISBN 0-7167-1456-6

[edit] External links

• Mineral Galleries: Chromite
• Webmineral.com
• Minerals.net
• USGS info.

Please help improve this article by expanding it. Further information might be found on the talk page. (September 2008)

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