Chrome ore Is an iron chromium oxide: Fe Cr2 O4 . 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 magnesia chromite (MgCr2 O4 ); substitution of aluminium occurs leading to hercynite (FeAl 2 O 4 ). It is by far the most industrially important mineral to produce metallic chromium, used as an alloying ingredient in stainless and tool steels.
Chromite Occurrence
Chromite is found as orth cumulate lenses of chromitite 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 Uses
The only ores of chromium are the minerals chromite and magnesia chromite. Most of the time, economic geology names chromite the whole chromite-magnesiochromite series: FeCr2 O4, (Fe,Mg)Cr2 O4 , (Mg,Fe)Cr2 O4 and MgCr2 O4. 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 (FeCr2 O4) is reduced with either aluminium or silicon in an aluminothermic reaction and for the production of pure chromium the iron has to be separated from the chromium in two step roasting and leaching process. Chromite is also used as a refractory material, because it has a high heat stability.
The chromium extracted from chromite is used in chrome plating and alloying for production of corrosion resistant superalloys, nichrome, and stainless steel. Chromium is used as a pigment for glass, glazes, and paint, and as an oxidizing agent for tanning leather. It is also sometimes used as a gemstone.
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