- Chromite
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Chromite 
General Category Oxide minerals Chemical formula (Fe, Mg)Cr2O4 Strunz classification 04.BB.05 Crystal symmetry Isometric hexoctahedral
H-M symbol: (4/m3 2/m)
Space group: F d3mUnit cell a = 8.344 Å; Z = 8 Identification Color Black to brownish black; brown to brownish black on thin edges in transmitted light Crystal habit Octahedral rare; massive to granular Crystal system Isometric Twinning Spinel law on {1ll} Cleavage None, parting may develop along {111} Fracture Uneven Tenacity Brittle Mohs scale hardness 5.5 Luster Submetallic Streak Brown Diaphaneity Translucent to opaque. Specific gravity 4.5 - 4.8 Optical properties Isotropic Refractive index n = 2.08-2.16 Other characteristics Weakly magnetic References [1][2][3][4] This article is about the mineral. For the chromium(III) anion and its salts, see Chromite (compound).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);[5] substitution of aluminium occurs leading to hercynite (FeAl2O4).[6]
Contents
Occurrence
Chromite is found in peridotite from the Earth's mantle. It also occurs in layered ultramafic intrusive rocks.[7] 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.[8] The Stillwater igneous complex in Montana also contains significant chromite.[2]
Uses
Chromite from Albania
The only ores of chromium are the minerals chromite and magnesiochromite. Most of the time, economic geology names chromite the whole chromite-magnesiochromite series: FeCr2O4, (Fe,Mg)Cr2O4, (Mg,Fe)Cr2O4 and MgCr2O4.[4] 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.[9]
Chromite is also used as a refractory material, because it has a high heat stability.[10]
Mining
Chromium ore output in 2002In 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.[11][12]
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.[citation needed]
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.[13]
In April 2010 the Government of Ontario announced[14] 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
- ^ http://www.handbookofmineralogy.com/pdfs/chromite.pdf Handbook of Mineralogy
- ^ a b Klein, Corneis and Cornelius S. Hurlbut, Manual of Mineralogy, Wiley, 20th ed., pp. 312-313 ISBN 0-471-80580-7
- ^ http://webmineral.com/data/Chromite.shtml Webmineral data
- ^ a b http://www.mindat.org/min-1036.html Mindat.org
- ^ http://www.mindat.org/min-8675.html Mindat
- ^ http://www.mindat.org/min-8674.html Mindat
- ^ Gu, F; Wills, B (1988). "Chromite- mineralogy and processing". Minerals Engineering 1 (3): 235. doi:10.1016/0892-6875(88)90045-3.
- ^ Guilbert, John M., and Park, Charles F., Jr. (1986) The Geology of Ore Deposits, Freeman, ISBN 0-7167-1456-6
- ^ Papp, John F.; Lipin Bruce R. (2006). "Chromite". Industrial Minerals & Rocks: Commodities, Markets, and Uses (7th ed.). SME. ISBN 9780873352338. http://books.google.com/?id=zNicdkuulE4C&pg=PA309.
- ^ Routschka, Gerald (2008). Pocket Manual Refractory Materials: Structure - Properties - Verification. Vulkan-Verlag. ISBN 9783802731587. http://books.google.com/?id=0ugkNtlWKWEC&pg=PA205.
- ^ Papp, John F.. "Mineral Commodity Summary 2006: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/chrommcs06.pdf. Retrieved 2009-02-24.
- ^ Papp, John F.. "Minerals Yearbook 2006: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/myb1-2006-chrom.pdf. Retrieved 2009-02-24.
- ^ "How Products are Made, Vol. 1". http://www.madehow.com/Volume-1/Stainless-Steel.html. Retrieved 29 Dec., 2010.
- ^ "YouTube - premierofontario's Channel". Youtube. http://www.youtube.com/user/premierofontario#p/u/6/7wkjwn7X5dE. Retrieved 2010-04-13.
External links
Ores Acanthite (silver) · Chalcopyrite (copper) · Chalcocite (copper) · Cinnabar (mercury) · Galena (lead) · Pentlandite (nickel) · Sphalerite (zinc)OtherOre deposit types Banded iron formation · Carbonate hosted lead zinc ore deposits · Heavy mineral sands · Iron oxide copper gold · Kambalda type komatiitic nickel ore deposits · Lateritic nickel · Magmatic nickel-copper-iron-PGE deposits · Porphyry copper · Sedimentary exhalative deposits · Volcanogenic massive sulfideCategories:- Magnesium minerals
- Iron minerals
- Chromium minerals
- Spinel group
- Refractory materials
- Cubic minerals
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