Chromite

Name	Chromite
Category	Oxide mineral
Formula	(Fe, Mg)Cr2O4
Color	Black to brownish black; brown to brownish black on thin edges in transmitted light
Habit	Octahedral rare; massive to granular
System	Isometric; hexoctahedral H-M Symbol (4/m 2/m) Space Group: F d3m
Cleavage	None, parting may develop along {111}
Fracture	Conchoidal
Mohs	5.5
Luster	Submetallic
Refractive	n == 2.08-2.16
Opticalprop	Isotropic
Streak	Dark brown
Gravity	4.5 - 4.8
Diaphaneity	Translucent to opaque.
Other	Weakly magnetic
References

Chromite is an iron chromium oxide: FeCr₂O₄. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr₂O₄); substitution of aluminium occurs leading to hercynite (FeAl₂O₄).

Occurrence

Chromite is found in peridotite from the Earth's mantle. It also occurs in layered ultramafic intrusive rocks. 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. The Stillwater igneous complex in Montana also contains significant chromite.

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

Mining

In 2002 14,600,000 metric tons of chromite were mined. The largest producers were 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.

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 other alloys.

In April 2010 the Government of Ontario announced that they would be opening up a large chromite deposit to development in the northern part of Ontario known as the Ring of Fire.

References

External links

Minerals.net

USGS info.

Category:Magnesium minerals Category:Iron minerals Category:Chromium minerals Category:Spinel group Category:Refractory materials Category:Cubic minerals