Chromite
Primary ore of chromium, essential for stainless steel production.
Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide, with the chemical formula FeCr2O4. It is an oxide mineral belonging to the spinel group and is mined particularly to make stainless steel through the production of ferrochrome, an iron-chromium alloy.
- chemical_formula
- FeCr2O4
- mineral_group
- Spinel group
- color
- Iron-black
- luster
- Metallic
- streak
- Dark brown
- hardness
- 5.5 on Mohs scale
- crystal_system
- Isometric (spinel group)
Lore & Background
Chromite grains are commonly found in large mafic igneous intrusions such as the Bushveld in South Africa and India. It occurs as massive and granular crystals, rarely as octahedral crystals, and twinning occurs on the {111} plane as described by the spinel law. Chromite can be seen in thin sections with disseminated euhedral to subhedral crystals. The mineral can change into different minerals based on the amounts of each element, forming a complete solid solution series with magnesiochromite, magnetite, and other spinel group members. Chromite forms early in the crystallization process and is resistant to alteration by high temperatures and pressures in metamorphic series.
Reader's Guide
Chromite is the principal source of chromium, used extensively in metallurgy, electroplating, paints, tanning, and paper production. The vast Bushveld Igneous Complex of South Africa contains layers consisting of 90% chromite, forming the rare rock type chromitite. Stratiform deposits in layered intrusions provide 98% of worldwide chromite reserves, with major deposits in South Africa, Canada, Finland, and Madagascar. Podiform deposits are found in Kazakhstan, Turkey, and Albania. Environmental contamination with hexavalent chromium (Cr(VI)) is a major health concern, as Cr(VI) is a highly toxic carcinogen. When chromite ore is exposed to surface conditions, trivalent chromium (Cr(III)) can convert to Cr(VI) through dry milling or grinding. Cr(III) is an essential nutrient for lipid and glucose metabolism, while Cr(VI) is rarely found in nature and is generally produced through human activity.
Did You Know?
- Chromite can form grains up to 3 cm in size, associated with stable supersaturated conditions in meteorite bodies.
- The Bushveld Igneous Complex in South Africa has layers consisting of 90% chromite, forming the rare rock type chromitite.
- Chromite is resistant to alteration effects of high temperatures and pressures in the metamorphic series, progressing unaltered.
- Stratiform deposits provide 90-95% of worldwide chromite reserves.
Frequently Asked Questions
Who is Chromite?
Chromite is an oxide mineral in the spinel group whose composition is iron(II) oxide combined with chromium(III) oxide, giving it the formula FeCr2O4. It is the principal ore mineral from which chromium is extracted.
What is Chromite's role in the mineral world?
Chromite is mined almost exclusively to produce ferrochrome, an iron-chromium alloy that serves as the key feedstock for stainless steel manufacturing. In that sense it acts as the gateway mineral for one of industry's most important alloys.
What does Chromite look like?
It appears as an iron-black mineral with a distinctly metallic sheen. When scratched across an unglazed porcelain tile it leaves a dark brown streak.
How hard is Chromite on the Mohs scale?
Chromite registers at 5.5, placing it roughly between apatite and orthoclase feldspar in hardness. That makes it moderately hard—hard enough to scratch glass but soft enough to be scratched by a steel nail.
Why is Chromite important to industry?
It is the primary natural source of chromium, the element responsible for giving stainless steel its corrosion resistance. Without chromite deposits, large-scale production of stainless steel and many other chromium-bearing alloys would be impractical.
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