Chromite is a crystalline

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...

composed primarily of

iron(II) oxide Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists ...

and

chromium(III) oxide Chromium(III) oxide (or chromia) is an inorganic compound with the formula . It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite. Structure and properties has the corundum ...

compounds. It can be represented by the chemical formula of FeCr₂O₄. It is an

oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the ...

belonging to the

spinel group The spinels are any of a class of minerals of general formulation which crystallise in the cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a cubic close-packed lattice and the cations ...

. The element

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

can substitute for

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

in variable amounts as it forms a

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

with magnesiochromite (MgCr₂O₄). A substitution of the element

aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...

can also occur, leading to

hercynite Hercynite is a spinel mineral with the formula FeAl2O4. It occurs in high-grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers. It was first descr ...

(FeAl₂O₄). Chromite today is mined particularly to make stainless steel through the production of

ferrochrome Ferrochrome, or ferrochromium (FeCr) is a type of ferroalloy, that is, an alloy of chromium and iron, generally containing 50 to 70% chromium by weight. Ferrochrome is produced by electric arc carbothermic reduction of chromite. Most of the gl ...

(FeCr), which is an iron-chromium alloy. Chromite grains are commonly found in large

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks includ ...

igneous intrusions such as the

Bushveld The Bushveld (from af, bosveld, af, bos 'bush' and af, veld) is a sub-tropical woodland ecoregion of Southern Africa. It encompasses most of Limpopo Province and a small part of the North West Province of South Africa, the Central and Nort ...

in South Africa and India. Chromite is iron-black in color with a metallic luster, a dark brown streak and a hardness on the Mohs scale of 5.5.

Properties

Chromite minerals are mainly found in mafic-ultramafic

igneous intrusions Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or l ...

and are also sometimes found in

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...

s. The chromite minerals occur in layered formations that can be hundreds of kilometres long and a few meters thick. Chromite is also common in

iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most i ...

s and form in association with silicates and

troilite Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe(1-x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency whic ...

minerals.

Crystal structure

The chemical composition of chromite can be represented as FeCr₂O₄, with the iron in the +2

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...

and the chromium in the +3 oxidation state. Chromite, when presented as an

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...

, or in massive form, forms as fine granular aggregates. The structure of the

can be seen as platy, with breakages along planes of weakness. Chromite can also be presented in a thin section. The grains seen in thin sections are disseminated with crystals that are

euhedral Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as '' xenomorphic'' or ''allotriomorphic''): a rock with an anhedra ...

to subhedral. Chromite contains Mg, ferrous iron e(II) Al and trace amounts of Ti. Chromite can change into different minerals based on the amounts of each element in the mineral. Chromite is a part of the

, which means that it is able to form a complete

series with other members in the same group. These include minerals such as chenmingite (FeCr₂O₄),

xieite Xieite is an iron chromium oxide mineral with formula Fe2+Cr2O4. It is a member of the spinel group and a high pressure polymorph of chromite. It was discovered in samples taken from the Suizhou meteorite which fell in 1986 in the Zengdu Distr ...

(FeCr₂O₄), magnesiochromite (MgCr₂O₄) and

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...

(Fe²⁺Fe³⁺₂O₄). Chenmingite and xieite are polymorphs of chromite while magnesiochromite and magnetite are

isostructural Isostructural chemical compounds have similar chemical structures. "Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous s ...

with chromite.

Crystal size and morphology

Chromite occurs as massive and granular crystals and very rarely as

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

crystals. Twinning for this mineral occurs on the plane as described by the spinel law. Grains of minerals are generally small in size. However, chromite grains up to 3 cm have been found. These grains are seen to crystallize from the liquid of a

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...

body where there are low amounts of chromium and oxygen. The large grains are associated with stable

supersaturated In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. Most commonly the term is applied to a solution of a solid in a liq ...

conditions seen from the meteorite body.

Reactions

Chromite is an important mineral in helping to determine the conditions that rocks form. It can have reactions with various gases such as CO and CO₂. The reaction between these gases and the solid chromite grains results in the reduction of the chromite and allows for the formation of iron and chromium

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...

s. There could also be a formation of metal

carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of th ...

s from the interaction with chromite and the gases. Chromite is seen to form early in the

crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely de ...

process. This allows for chromite to be resistant to the alteration effects of high temperatures and pressures seen in the

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...

series. It is able to progress through the

series unaltered. Other minerals with a lower resistance are seen to alter in this series to minerals such as serpentine,

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more alum ...

and

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...

Distribution of deposits

Chromite is found as orthocumulate lenses in

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...

from the Earth's mantle. It also occurs in layered,

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are compos ...

intrusive rocks. In addition, it is found in metamorphic rocks such as some

serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''ser ...

Ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...

deposits of chromite form as early magmatic differentiates. It is commonly associated with

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

, serpentine and

corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the ...

. The vast

Bushveld Igneous Complex The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

is a large layered

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

body with some layers consisting of 90% chromite, forming the rare rock type

chromitite Chromitite is an igneous cumulate rock composed mostly of the mineral chromite. It is found in layered intrusions such as the Bushveld Igneous Complex in South Africa, the Stillwater igneous complex in Montana and the Ring of Fire discovery in ...

(cf. chromite the mineral and chromitite, a rock containing chromite). The

Stillwater Igneous Complex The Stillwater igneous complex is a large layered mafic intrusion (LMI) located in southern Montana in Stillwater, Sweet Grass and Park Counties. The complex is exposed across 30 miles (48 km) of the north flank of the Beartooth Mount ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

also contains significant chromite. Chromite suitable for commercial mining is found in just a handful of very substantial deposits. There are 2 main types of chromite deposits: stratiform deposits and podiform deposits. Stratiform deposits in layered intrusions are the main source of chromite resources and are found in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bo ...

, and

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

. Chromite resources from podiform deposits are mainly found in

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia Russia (, , ), or the Russian Federation, is a transcontinental coun ...

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...

, and

Albania Albania ( ; sq, Shqipëri or ), or , also or . officially the Republic of Albania ( sq, Republika e Shqipërisë), is a country in Southeastern Europe. It is located on the Adriatic The Adriatic Sea () is a body of water separating the ...

Zimbabwe Zimbabwe (), officially the Republic of Zimbabwe, is a landlocked country located in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Botswana to the south-west, Zambia to the north, and Mozam ...

is the only country that contains notable chromite reserves in both stratiform and podiform deposits.

Stratiform deposits

Stratiform deposits are formed as large sheet-like bodies, usually formed in layered

complexes. This type of deposit is used to obtain 98% of the worldwide chromite reserves. Stratiform deposits are typically seen to be of

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...

in age and are found in

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

s. The

provinces that these deposits are formed in were likely intruded into

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial' ...

, which may have contained

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies und ...

s or

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es. The shapes of these intrusions are described as tabular or funnel-shaped. The tabular intrusions were placed in the form of sills with the layering of these intrusions being parallel. Examples of these tabular intrusions can be seen in the

and

Bird River The Bird River is a tidal river in eastern Baltimore County, Maryland, Baltimore County in the U.S. state of Maryland. The Bird River empties into the Gunpowder River. See also *List of Maryland rivers References External linksNOAA nautical ch ...

. The funnel-shaped intrusions are seen to be dipping towards the center of the intrusion. This gives the layers in this intrusion a

syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...

formation. Examples of this type of intrusion can be seen in the

and the

Great Dyke The Great Dyke is a linear geological feature that trends nearly north-south through the centre of Zimbabwe passing just to the west of the capital, Harare. It consists of a band of short, narrow ridges and hills spanning for approximately . The ...

. Chromite can be seen in stratiform deposits as multiple layers which consist of

. Thicknesses for these layers range between 1 cm to 1 m. Lateral depths can reach lengths of 70 km. Chromitite is the main rock in these layers, with 50–95% of it being made of chromite and the rest being composed of

orthopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

clinopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

, and the various alteration products of these minerals. An indication of water in the magma is determined by the presence of brown

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

Podiform deposits

Podiform deposits are seen to occur within the

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found ...

sequences. The stratigraphy of the ophiolite sequence is deep-ocean sediments,

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of disconti ...

s, sheeted dykes,

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...

s and

tectonite Tectonites are metamorphic or tectonically deformed rocks whose fabric reflects the history of their deformation, or rocks with fabric that clearly displays coordinated geometric features that indicate continuous solid (ductile) flow during f ...

s. These deposits are found in ultramafic rocks, most notably in tectonites. It can be seen that the abundance of podiform deposits increase towards the top of the tectonites. Podiform deposits are irregular in shape. "Pod" is a term given by geologists to express the uncertain morphology of this deposit. This deposit shows

foliation In mathematics ( differential geometry), a foliation is an equivalence relation on an ''n''-manifold, the equivalence classes being connected, injectively immersed submanifolds, all of the same dimension ''p'', modeled on the decomposition ...

that is parallel to the foliation of the host rock. Podiform deposits are described as discordant, subconcordant and concordant. Chromite in podiform deposits form as anhedral grains. The ores seen in this type of deposit have nodular texture and are loosely-packed nodules with a size range of 5–20 mm. Other minerals that are seen in podiform deposits are

pargasite Pargasite is a complex inosilicate mineral of the amphibole group with formula NaCa2(Mg4Al)(Si6Al2)O22(OH)2. It was first described for an occurrence in Pargas, Finland in 1814 and named for the locality. It occurs in high temperature regional ...

, Na-mica,

albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilica ...

, and

jadeite Jadeite is a pyroxene mineral with composition Na Al Si2 O6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, but is most often found in shades ...

Health and environmental impacts

Chromium extracted from chromite is used on a large scale in many industries, including metallurgy, electroplating, paints, tanning, and paper production. Environmental contamination with hexavalent chromium is a major health and environmental concern. Chromium is most stable in its

trivalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of a ...

(Cr(III)) form, seen in stable compounds such as natural ores. Cr(III) is an essential nutrient, required for

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids incl ...

and

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...

metabolism in animals and humans. In contrast, the second most stable form,

hexavalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of an ...

chromium (Cr(VI)), is generally produced through human activity and rarely seen in nature (as in

crocoite Crocoite is a mineral consisting of lead chromate, Pb Cr O4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment. Description Crocoite is commonl ...

), and is a highly toxic carcinogen that may kill animals and humans if ingested in large doses. Health effects When chromite

is mined, it is aimed for the production of

and produces a chromite

concentrate A concentrate is a form of substance that has had the majority of its base component (in the case of a liquid: the solvent) removed. Typically, this will be the removal of water from a solution or suspension, such as the removal of water from fru ...

of a high chromium to iron ratio. It can also be crushed and processed. Chromite concentrate, when combined with a

reductant In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

such as

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

coke Coke usually refers to: * Coca-Cola, a brand of soft drink **The Coca-Cola Company * Slang term for cocaine, a psychoactive substance and illicit drug Substances Soft drinks * Cola, any soft drink similar to Coca-Cola * Generic name for a soft d ...

and a high temperature furnace can produce

. Ferrochrome is a type of

ferroalloy Ferroalloy refers to various alloys of iron with a high proportion of one or more other elements such as manganese (Mn), aluminium (Al), or silicon (Si). They are used in the production of steels and alloys. The alloys impart distinctive qualiti ...

that is an

in between chromium and iron. This ferroalloy, as well as chromite

can introduce various health effects. Introducing a definitive control approach and distinct mitigation techniques can provide importance related to the safety of human health. When chromite ore is exposed to surface conditions,

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movemen ...

and

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

can occur. The element chromium is most abundant in chromite in the form of trivalent (Cr-III). When chromite

is exposed to aboveground conditions, Cr-III can be converted to Cr-VI, which is the hexavalent state of chromium. Cr-VI is produced from Cr-III by means of dry

milling Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using rota ...

or grinding of the ore. This is due to the moistness of the milling process as well as the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

in which the milling is taking place. A wet environment and a non-oxygenated atmosphere are ideal conditions to produce less Cr-VI, while the opposite is known to create more Cr-VI.''Potential Toxic Effects of Chromium, Chromite Mining and Ferrochrome Production : A Literature Review''. MiningWatch Canada. 2012 (PDF). May 2012.https://miningwatch.ca/sites/default/files/chromite_review.pdf Production of

Ferrochrome Ferrochrome, or ferrochromium (FeCr) is a type of ferroalloy, that is, an alloy of chromium and iron, generally containing 50 to 70% chromium by weight. Ferrochrome is produced by electric arc carbothermic reduction of chromite. Most of the gl ...

is observed to emit

pollutants A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

into the air such as

nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide * Nitrogen trioxide (), or ...

, carbon oxides and

sulfur oxides Sulfur oxide refers to many types of sulfur and oxygen containing compounds such as SO, SO2, SO3, S7O2, S6O2, S2O2, etc. Sulfur oxide (SO''x'') refers to one or more of the following: * Lower sulfur oxides (S''n''O, S7O2 and S6O2) * Sulfur mono ...

, as well as dust

particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The ...

with a high concentration of

heavy metals upright=1.2, Crystals of lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as metals with relatively high density, densities, atomi ...

such as

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and h ...

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

and

cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...

. During high temperature

smelting Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a ...

of chromite

to produce

, Cr-III is converted to Cr-VI. As with chromite ore, Ferrochrome is milled and therefore produces Cr-VI. Cr-VI is therefore introduced into the dust when the

is produced. This introduces health risks such as inhalation potential and

leaching Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to: *Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amoun ...

of toxins into the environment. Human exposure to chromium is ingestion, skin contact, and inhalation. Chromium-III and VI will accumulate in the tissues of humans and animals. The excretion of this type of chromium from the body tends to be very slow which means that elevated concentrations of chromium can be seen decades later in human tissues. Environmental effects Chromite mining, chromium, and ferrochome production can toxically effect the environment. Chromite

mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...

is necessary when it comes to the production of economic

commodities In economics, a commodity is an economic good, usually a resource, that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them. The price of a co ...

. As a result of leaching of soils and the explicit discharge from industrial activities,

of rocks that contain chromium will enter the water column. The route of chromium uptake in plants is still ambiguous, but because it is a nonessential element, chromium will not have a distinct mechanism for that uptake which is independent from chromium speciation. Plant studies have shown that toxic effects on plants from chromium include things such as wilting, narrow leaves, delayed or reduced growth, a decrease in

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...

production, damage to root membranes, small root systems, death and many more. Chromium's structure is similar to other essential elements which means that it can impact the mineral nutrition of plants. Chromitite Bushveld South Africa

During industrial activities and production things such as sediment, water, soil, and air all become polluted and contaminated with chromium. Hexavalent chromium has negative impacts towards soil ecology because it decreases soil micro-organism presence, function, and diversity. Chromium concentrations in soil diversify depending on the different compositions of the sediments and rocks that the soil is made from. The chromium present in soil is a mixture of both Cr(VI) and Cr(III). Certain types of chromium such as Chromium-VI has the capability to pass into the cells of organisms. Dust particles from industry operations and industrial wastewater contaminate and pollute surface water, groundwater, and soils. In aquatic environments, chromium could experience things such as

dissolution Dissolution may refer to: Arts and entertainment Books * ''Dissolution'' (''Forgotten Realms'' novel), a 2002 fantasy novel by Richard Lee Byers * ''Dissolution'' (Sansom novel), a 2003 historical novel by C. J. Sansom Music * Dissolution, in mu ...

sorption Sorption is a physical and chemical process by which one substance becomes attached to another. Specific cases of sorption are treated in the following articles: ; Absorption: "the incorporation of a substance in one state into another of a dif ...

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

, reduction, and

desorption Desorption is the physical process where a previously adsorbed substance is released from a surface. This happens when a molecule gains enough energy to overcome the activation barrier of the bounding energy that keeps it in the surface. There ...

. In aquatic ecosystems chromium bioaccumulates in invertebrates, aquatic plants, fish, and algae. These toxic effects will operate differently because things such as sex, size, and the development stage of an organism may vary. Things such as the temperature of the water, its alkalinity, salinity, pH, and other contaminants will also impact these toxic effects on organisms. Toxicology tests done in labs on rats and mice provides information on the doses of chromium in food or water which produces health problems in mammals such as reproductive harm, reduced growth and survival, behavioural changes, and cancer. Chromium is critical for good health since sufficient amounts should help with

glucose intolerance Prediabetes is a component of the metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesit ...

in humans. Studies showed that

chromium supplements Chromium deficiency is described as the consequence of an insufficient dietary intake of the mineral chromium. Chromium was first proposed as an essential element for normal glucose metabolism in 1959, and was widely accepted as being such by th ...

can be beneficial for people with insulin resistance and

type two diabetes Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urination ...

. Chromium lowers glucose levels and it enhances insulin sensitivity. Some studies also showed that chromium can help with

polycystic ovary syndrome Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and n ...

(PCOS). Excellent dietary sources include things such as wheat germ, broccoli, organ meats, and mushrooms.

Applications

Chromite can be used as a

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase ...

material, because it has a high

heat stability In materials science and molecular biology, thermostability is the ability of a substance to resist irreversible change in its chemical or physical structure, often by resisting decomposition or polymerization, at a high relative temperatur ...

. The chromium extracted from chromite is used in

chrome plating Chrome plating (less commonly chromium plating) is a technique of electroplating a thin layer of chromium onto a metal object. A chrome-plated item is called ''chrome''. The chromed layer can be decorative, provide corrosion resistance, ease o ...

and alloying for production of corrosion resistant

superalloy A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...

nichrome Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of alloys of nickel, chromium, and often iron (and possibly other elements) commonly used as resistance wire, heating elements in devices like toasters, electrical kettl ...

, and stainless steel. Chromium is used as a

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic comp ...

for glass, glazes, and paint, and as an

oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

for tanning leather. It is also sometimes used as a gemstone. Usually known as chrome, it is a very essential industrial metal. It is hard and resistant to corrosion. This is used for things such as nonferrous alloys, the production of stainless steel, chemicals that process leather, and the creation of pigments. Stainless steel usually contains about 18 percent of chromium. The chromium in the stainless steel is the material which hardens making it resilient to corrosion. A lot of car design like decorations are chromium plated. Superalloys that contain chromium allow jet engines to run under high-high stress, in a chemically oxidizing environment, and in high-temperature situations.

Porcelain tile pigmentation

Porcelain tile Porcelain tiles or ceramic tiles are porcelain or ceramic tiles commonly used to cover floors and walls, with a water absorption rate of less than 0.5 percent. The clay used to build porcelain tiles is generally denser. They can either be ...

s are often produced with many different colours and

ations. The usual contributor to colour in fast-fired porcelain tiles is black pigment, which is fairly expensive and is

synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic o ...

. Natural chromite allows for an inexpensive and inorganic pigmentation alternative to the expensive and allows for the

microstructure Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymers ...

and mechanical properties of the tiles to not be substantially altered or modified when introduced.

Gallery of chromite mineral specimens

File:Chromite-201529.jpg,

Octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

chromite crystal from the Freetown Layered Complex in

Sierra Leone Sierra Leone,)]. officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered by Liberia to the southeast and Guinea surrounds the northern half of the nation. Covering a total area of , Sierra ...

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

(size: 1.3 x 1.2 x 1.2 cm) File:Chromite by petrographic microscope.jpg, Chromite sample under a

petrographic microscope A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology wh ...

in plain polarized light (PPL) File:Chromite calcite uvarovit.jpg, Chromite grains with white

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scra ...

grains File:Chromite-pas-63b.jpg, Green oxide of chromium from

Baltimore Baltimore ( , locally: or ) is the List of municipalities in Maryland, most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic (United States), Mid-Atlantic, and List of United States cities by popula ...

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; ...

File:Chromite-468934.jpg, Large, equant chromite crystals from Hangha,

Kenema District Kenema District is a district in the Eastern Province of Sierra Leone. Its capital city, capital and largest city is Kenema, which is the third most populous city in Sierra Leone, after Freetown and Bo. Tongo is the second most populous city in ...

, Eastern Province,

References

External links

Minerals.net

USGS info.
{{Authority control Chromium minerals Cubic minerals Minerals in space group 227 Iron(II) minerals Magnesium minerals Spinel group Spinel gemstones Refractory materials