Chromite belongs to the group of oxides, spinel subgroup, has the formula FeCr2O4, chemically made up of 32% FeO and 68% Cr2O. Formed by magmatic differentiation, associated with minerals such as olivine, serpentine and corundum. It is the only source of extraction of chromium, which is widely used in general industry.
Characteristics and physical properties
| chromite | Characteristics and physical properties |
| class, group | Oxide, in the spinel group |
| Brightness | metallic to submetallic |
| Color | Greyish black to brownish black |
| Stripe | Dark brown |
| Tenacity | Fragile |
| Chemical formula | FeCr2O4 |
| Chemical composition | FeO=32%; Cr2O=68% |
| Hardness | 5.5 |
| Specific weight or density | 4.5 to 4.8 g/cm3 |
| cleavage | None, does not present |
| Fracture | Irregular |
| crystalline system | cubic, hexaoctahedral |
| Way of introducing yourself (habit) | Octahedral, solid, granular, compact |
| Origin and geological environment | Orthomagmatic, associated with ultrabasic rocks |
| associated rocks | Basic to ultrabasic igneous, metamorphic rocks |
| Associated minerals | Olivine, serpentine, corundum |
| Applications | Chromium ore, refractory material, manufacturing industry |
The chromite It is a dark greyish mineral, often in brownish-black tones, accompanied by a metallic luster that is difficult to observe, its streak is dark brown.
Formed as one of the first minerals to separate from magma, its chemical composition is FeCr2O4, where FeO represents 32%, and Cr2O 68%.
Its crystalline system is cubic hexaoctahedral, which gives it a characteristic octahedral habit; however, it is common to find massive, granular or compact crystals. It fractures irregularly and does not show any visible cleavage.
It has an average hardness of 5.5, its tenacity is brittle and its density is medium to high, almost 4.6 gr/cm3, this property especially differentiates it from other similar compounds such as ilmentite and magnetite.
Its mineral paragenesis associates it with magmas of ultrabasic to basic composition, which is why it is associated with olivine, serpentine, corundum, magnetite, and ilmentite, among others.
It is an important mineral in the manufacturing industry, since it is the only source of large-scale extraction of chromium.
Origin, formation and geological environment.
It is a constituent of peridotites and serpentines (ultrabasic rocks), since its formation occurs in the first stages of magmatic differentiation; however, it is also formed in sedimentary deposits such as beach sands and in foot-shaped deposits of metamorphic rocks derived from the alteration of the peridotites and norites.
Due to the type of magma from which they originate, their mineral paragenesis includes olivine, magnetite, plagioclase, ilmentite, serpentine, corundum.
The great deposits of chromite They are generally stratiform, that is, large masses of igneous rock that cool very slowly in subsurface magma chambers. Most of the world’s production comes from the Bushveld complex in South Africa and the Great Dam in Zimbabwe.
How to identify the Chromite?
Its identification can be a problem, all the main physical properties must be observed in an exhaustive way to differentiate it from other metallic minerals.
The hardness, the specific weight must be measured with precision, the brown stripe is a characteristic of this mineral. The submetallic luster and magnetism contrast also helps a lot in its differentiation from very similar metals like ilmentite and magnetite.
Chromite Uses
- As the only large-scale source of chromium in industry, this metal is highly prized by geologists and researchers.
- They are grouped into three categories: metallurgical, refractory, and chemical.
- Its most widespread use is given as an inducer of hardness, toughness and chemical resistance to steel, with which “stainless steel” is produced.
- It is also used for the production of superalloys that coat materials in conditions such as high temperatures, corrosives and high mechanical stress, such as jet engines.
- It is also used as a pigment for the industry in general, small amounts are also mixed in the crystallization of many minerals and precious stones.
The importance of chromite
It is a common mineral in all meteorites, except in carbonaceous chondrites and in basalts of lunar maria.
Due to its great importance in the development of the industry, it is a highly desired mineral in the strategic sector of the great world powers, its large reserves are strongly protected and there are emergency deposits for possible armed conflicts.