Chromite is an iron chromium oxide: FeCr2O4. It is the principal ore of chromium, a brownish-black oxide of chromium and iron. 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 aluminum occurs leading to hercynite (FeAl2O4).
Chromium is an important metal and has a wide range of industrial uses. It is by far the most industrially important mineral for the production of metallic chromium, used as an alloying ingredient in stainless and tool steels.
General Information
- Category: Oxide minerals (Spinel group)
- Formula: (Fe, Mg)Cr2O4
- Crystal system: Isometric
- Crystal class: Hexoctahedral (m3m)
Properties
It is dark gray to black in color with a metallic to submetallic luster and a high specific gravity. It occurs in basic and ultrabasic igneous rocks and in the metamorphic and sedimentary rocks that are produced when chromite-bearing rocks are altered by heat or weathering.
- Color: Black to brownish black; brown to brownish black on thin edges in transmitted light
- Crystal habit: Octahedral rare; massive to granular
- 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
Occurrences
Chromite is found as orthocumulate 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. An Ore deposit of chromite form as early magmatic differentiates. It is commonly associated with olivine, magnetite, serpentine, and corundum.
Chromite is important because it is the only economic ore of chromium, an essential element for a wide variety of metal, chemical, and manufactured products. Many other minerals contain chromium, but none of them are found in deposits that can be economically mined to produce chromium.
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