Chromite is an iron chromium oxide: FeCr2O4. It is an oxid 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).
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.
Properties of Chromite
Chromite can be challenging to identify. Several properties must be considered to differentiate it from other metallic ores. Hand specimen identification of chromite requires a consideration of: color, specific gravity, luster, and a characteristic brown streak. The most important clue to identifying chromite is its association with ultrabasic igneous rocks and metamorphic rocks such as serpentinite.
Chromite is sometimes slightly magnetic. This can cause it to be confused with magnetite. Chromite and ilmenite have very similar properties. Careful observations of hardness, streak, and specific gravity are required to distinguish these minerals in hand specimens.