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Iron () is a
chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo du ...
with
symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), m ...
Fe (from la,
ferrum Ferrum can refer to: *Iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the peri ...
) and
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
26. It is a
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
that belongs to the
first transition series In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations tha ...
and
group 8Group 8 may refer to: * Group 8 element, a series of elements in the Periodic Table * Group 8 Rugby League, a rugby league competition * Group 8 (Sweden), a feminist movement in Sweden * Group VIII, former nomenclature for the noble gases * The best ...
of the
periodic table The periodic table, also known as the periodic table of (the) chemical elements, is a tabular display of the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...

periodic table
. It is,
by mass, the most common element
by mass, the most common element
on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, right in front of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
(32.1% and 30.1%, respectively), forming much of Earth's outer and
inner core Earth's inner core is the innermost structure of Earth, geologic layer of planet Earth. It is primarily a solid ball (mathematics), ball with a radius of about , which is about 20% of Earth radius, Earth's radius or 70% of the Moon's radius. Th ...
. It is the fourth most common element in the Earth's crust. In its metallic state, iron is rare in the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), ...
, limited mainly to deposition by
meteorites A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies ...

meteorites
.
Iron ore Iron ores are rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it i ...
s, by contrast, are among the most abundant in the Earth's crust, although extracting usable metal from them requires
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...

kiln
s or
furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (house heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler Poland ...
s capable of reaching or higher, about 500 °C (900 °F) higher than that required to
smelt Smelt may refer to: * Smelting, chemical process *The common name of various fish ** Smelt (fish), a family of small fish, Osmeridae ** Australian smelt in the family Retropinnidae and species ''Retropinna semoni'' ** Big-scale sand smelt ''Atherin ...
copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

copper
. Humans started to master that process in
Eurasia Eurasia () is the largest continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a ...

Eurasia
during the
2nd millennium BCE The 2nd millennium BC spanned the years 2000 through 1001 BC. In the Ancient Near East, it marks the transition from the Middle to the Late Bronze Age. The Ancient Near Eastern cultures are well within the historical era: The first half of the m ...
and the use of iron
tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment. Although many animals use tool use by animals, simple tools, only human beings, whose use of stone tools dates back Paleolithic, hun ...

tool
s and
weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict physical damage or harm. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, self-defe ...
s began to displace
copper alloys Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...
, in some regions, only around 1200 BCE. That event is considered the transition from the
Bronze Age The Bronze Age is a prehistoric Periodization, period that was characterized by the use of bronze, in some areas proto-writing, and other early features of urban civilization. The Bronze Age is the second principal period of the Three-age sys ...
to the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history Human history, or world history, is the narrative of Human, humanity's pa ...
. In the
modern world Human history, or world history, is the narrative of Human, humanity's past. It is understood through archaeology, anthropology, genetics, and linguistics, and since the History of writing, advent of writing, from primary source, primary and ...
, iron alloys, such as
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appe ...

steel
,
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
,
cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impuritie ...
and special steels are by far the most common industrial metals, because of their mechanical properties and low cost. The iron and steel industry is thus very important economically, and iron is the cheapest metal, with a price of a few dollars per kilogram or per pound (see Metal#uses). Pristine and smooth pure iron surfaces are mirror-like silvery-gray. However, iron reacts readily with
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
and
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
to give brown to black
hydrate In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...
d
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
s, commonly known as
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous ferric oxides, hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxi ...

rust
. Unlike the oxides of some other metals, that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing fresh surfaces for corrosion. Although iron readily reacts, high purity iron, called electrolytic iron, has better corrosion resistance. The body of an adult human contains about 4 grams (0.005% body weight) of iron, mostly in
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
and
myoglobin Myoglobin (symbol Mb or MB) is an iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their ...

myoglobin
. These two
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s play essential roles in
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
, respectively
oxygen transport Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear s ...

oxygen transport
by
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
and oxygen storage in
muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cat ...

muscle
s. To maintain the necessary levels,
human iron metabolism Human iron metabolism is the set of chemical reactions that maintain human homeostasis of iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to ...
requires a minimum of iron in the diet. Iron is also the metal at the active site of many important
redox Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

redox
enzymes Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...
dealing with
cellular respiration Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such a ...

cellular respiration
and oxidation and reduction in plants and animals. Chemically, the most common oxidation states of iron are
iron(II) In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
and iron(III). Iron shares many properties of other
transition metal In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations tha ...
s, including the other
group 8 element Group 8 is a group (column) of chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all h ...
s,
ruthenium Ruthenium is a chemical element with the Symbol (chemistry), symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to ...

ruthenium
and
osmium Osmium (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximat ...

osmium
. Iron forms compounds in a wide range of
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge ...
s, −2 to +7. Iron also forms many
coordination compound A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing ...
s; some of them, such as
ferrocene Ferrocene is an organometallic chemistry, organometallic compound with the formula . The molecule is a Cyclopentadienyl complex, complex consisting of two Cyclopentadienyl anion, cyclopentadienyl rings bound to a central iron atom. It is an oran ...

ferrocene
,
ferrioxalate Ferrioxalate or trisoxalatoferrate(III) is a valence (chemistry), trivalent anion with formula . It is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions anions acting as ligands. Th ...

ferrioxalate
, and
Prussian blue Prussian blue (also known as Berlin blue or, in painting Painting is the practice of applying paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, ...

Prussian blue
, have substantial industrial, medical, or research applications.


Characteristics


Allotropes

At least four allotropes of iron (differing atom arrangements in the solid) are known, conventionally denoted α, γ, δ, and ε. The first three forms are observed at ordinary pressures. As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a
body-centered cubic In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' " ...
(bcc)
crystal structure In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "co ...

crystal structure
. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a
face-centered cubic 200px, A network model of a primitive cubic system In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived fro ...

face-centered cubic
(fcc) crystal structure, or
austenite 250px, Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron I ...
. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. The physical properties of iron at very high pressures and temperatures have also been studied extensively, because of their relevance to theories about the cores of the Earth and other planets. Above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another
hexagonal close-packed In geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relative position of ...
(hcp) structure, which is also known as ε-iron. The higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa and temperatures of at least 1500 K. It is supposed to have an
orthorhombic In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "col ...

orthorhombic
or a double hcp structure. (Confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure has not changed.) The
inner core Earth's inner core is the innermost structure of Earth, geologic layer of planet Earth. It is primarily a solid ball (mathematics), ball with a radius of about , which is about 20% of Earth radius, Earth's radius or 70% of the Moon's radius. Th ...
of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
is generally presumed to consist of an iron-
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
alloy An alloy is an admixture of metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in ...
with ε (or β) structure.


Melting and boiling points

The melting and boiling points of iron, along with its
enthalpy of atomization The enthalpy of atomization (also atomisation in British English) is the enthalpy change that accompanies the total separation of all atoms An atom is the smallest unit of ordinary matter that forms a chemical element Image:Simple Periodi ...
, are lower than those of the earlier 3d elements from
scandium Scandium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

scandium
to
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus;Greenwood and Earnshaw, p. 1116 however, they are higher than the values for the previous element
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
because that element has a half-filled 3d sub-shell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium. The melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, published data (as of 2007) still varies by tens of gigapascals and over a thousand kelvin.


Magnetic properties

Below its
Curie point In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...
of 770 °C, α-iron changes from
paramagnetic Paramagnetism is a form of magnetism Magnetism is a class of physical attributes that are mediated by magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, a ...
to
ferromagnetic Ferromagnetism is the basic mechanism by which certain materials (such as iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), formi ...
: the spins of the two unpaired electrons in each atom generally align with the spins of its neighbors, creating an overall
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
. This happens because the orbitals of those two electrons (d''z''2 and d''x''2 − ''y''2) do not point toward neighboring atoms in the lattice, and therefore are not involved in metallic bonding. In the absence of an external source of magnetic field, the atoms get spontaneously partitioned into
magnetic domain A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moment The magnetic moment is the magnetic strength and orientation of a magnet or other obje ...
s, about 10 micrometers across, such that the atoms in each domain have parallel spins, but some domains have other orientations. Thus a macroscopic piece of iron will have a nearly zero overall magnetic field. Application of an external magnetic field causes the domains that are magnetized in the same general direction to grow at the expense of adjacent ones that point in other directions, reinforcing the external field. This effect is exploited in devices that needs to channel magnetic fields, such as electrical transformers,
magnetic recording Magnetic storage or magnetic recording is the storage of data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sense, data are a set of values of qualitative property, qualitative or qu ...
heads, and s. Impurities,
lattice defect Lattice may refer to: Arts and design * Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material * Lattice (music), an organized grid model of pitch ratios * Lattice (pastry) A cher ...
s, or grain and particle boundaries can "pin" the domains in the new positions, so that the effect persists even after the external field is removed — thus turning the iron object into a (permanent)
magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a ve ...

magnet
. Similar behavior is exhibited by some iron compounds, such as the ferrites including the mineral
magnetite Magnetite is a 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 for ...

magnetite
, a crystalline form of the mixed iron(II,III) oxide (although the atomic-scale mechanism,
ferrimagnetism A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism. For ferrimagnetic materials, these moments are unequal in magnitude so a spontaneous magnetization remains. This can ...
, is somewhat different). Pieces of magnetite with natural permanent magnetization (
lodestone of the Smithsonian Image:Lodestone (black).jpg, Lodestone attracting small bits of iron A lodestone is a naturally magnetized piece of the mineral magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and min ...
s) provided the earliest
compass A compass is a device that shows the cardinal direction The four cardinal directions, or cardinal points, are the directions north, east, south, and west, commonly denoted by their initials N, E, S, and W. East and west are perpendicular ( ...

compass
es for navigation. Particles of magnetite were extensively used in magnetic recording media such as core memories,
magnetic tape Magnetic tape is a medium for , made of a thin, magnetizable coating on a long, narrow strip of . It was developed in Germany in 1928, based on . Devices that record and playback audio and video using magnetic tape are s and s respectively. A ...

magnetic tape
s, , and
disk Disk or disc may refer to: * Disk (mathematics) * Disk storage Music * Disc (band), an American experimental music band * Disk (album), ''Disk'' (album), a 1995 EP by Moby Other uses * Disc (galaxy), a disc-shaped group of stars * Disc (magazin ...

disk
s, until they were replaced by
cobalt Cobalt is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

cobalt
-based materials.


Isotopes

Iron has four stable
isotope Isotopes are two or more types of atoms that have the same atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of ...
s: 54Fe (5.845% of natural iron), (91.754%), 57Fe (2.119%) and 58Fe (0.282%). 20-30 artificial isotopes have also been created. Of these stable isotopes, only 57Fe has a
nuclear spin In nuclear physics, atomic physics, and nuclear chemistry, the nuclear shell model is a nuclear model, model of the atomic nucleus which uses the Pauli exclusion principle to describe the structure of the nucleus in terms of energy levels. The f ...
(−). The
nuclide A nuclide (or nucleide, from nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic c ...

nuclide
54Fe theoretically can undergo
double electron capture Double electron capture is a decay mode Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sm ...
to 54Cr, but the process has never been observed and only a lower limit on the half-life of 3.1×1022 years has been established. 60Fe is an
extinct radionuclide An extinct radionuclide is a radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any sub ...
of long
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies ...
(2.6 million years). It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide . Much of the past work on isotopic composition of iron has focused on the
nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...
of 60Fe through studies of
meteorite A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces ...
s and ore formation. In the last decade, advances in
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio The mass-to-charge ratio (''m''/''Q'') is a physical quantity A physical quantity is a physical property of a material or system that can be Quant ...
have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the
stable isotope The term stable isotope has a meaning similar to stable nuclide Stable nuclides are nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of proton A proton is a subat ...
s of iron. Much of this work is driven by the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...
and
planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), Astronomical object, celestial bodies (such as Natural satellite, moons, Asteroid, asteroids, Comets on Fire, comets) and planetary systems (in p ...
communities, although applications to biological and industrial systems are emerging. In phases of the meteorites ''Semarkona'' and ''Chervony Kut,'' a correlation between the concentration of 60Ni, the granddaughter of 60Fe, and the abundance of the stable iron isotopes provided evidence for the existence of 60Fe at the time of
formation of the Solar System The formation and evolution of the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all indi ...
. Possibly the energy released by the decay of 60Fe, along with that released by , contributed to the remelting and
differentiation Differentiation may refer to: Business * Differentiation (economics), the process of making a product different from other similar products * Product differentiation, in marketing * Differentiated service, a service that varies with the identity o ...
of
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observ ...

asteroid
s after their formation 4.6 billion years ago. The abundance of 60Ni present in
extraterrestrial Extraterrestrial refers to any object or being beyond (wikt:extra-, extra-) the planet Earth (wikt:terrestrial, terrestrial). It is derived from the Latin words wikt:extra, ''extra'' ("outside", "outwards") and ''terrestris'' ("earthly", "of or rela ...
material may bring further insight into the origin and early history of the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
. The most abundant iron isotope 56Fe is of particular interest to nuclear scientists because it represents the most common endpoint of
nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...
. Since 56Ni (14
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
s) is easily produced from lighter nuclei in the
alpha process The alpha process, also known as the alpha ladder, is one of two classes of nuclear fusion reactions by which stars convert helium into heavier elements, the other being the triple-alpha process. The triple-alpha process consumes only helium, and ...
in
nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a t ...
s in supernovae (see
silicon burning processIn astrophysics Astrophysics is a science that employs the methods and principles of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural ...
), it is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle, resulting in 60Zn, requires a great deal more energy. This 56Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in the
supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
gas cloud, first to radioactive 56Co, and then to stable 56Fe. As such, iron is the most abundant element in the core of
red giant A red giant is a luminous giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Ast ...

red giant
s, and is the most abundant metal in
iron meteorite Iron meteorites, also known as siderite :''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known ...
s and in the dense metal cores of planets such as
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
.Greenwood and Earnshaw, p. 12 It is also very common in the universe, relative to other stable
metals A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Electrical resistivity and conductivity, e ...
of approximately the same
atomic weight Relative atomic mass (symbol: ''A'') or atomic weight is a dimensionless physical quantity A physical quantity is a physical property of a material or system that can be Quantification (science), quantified by measurement. A physical quantity ...
. Iron is the sixth most abundant element in the
universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development ...

universe
, and the most common
refractory 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 temperature Temperature ( ) is a physical quantity that expresses hot and ...
element. Although a further tiny energy gain could be extracted by synthesizing , which has a marginally higher binding energy than 56Fe, conditions in stars are unsuitable for this process. Element production in supernovas and distribution on Earth greatly favor iron over nickel, and in any case, 56Fe still has a lower mass per nucleon than 62Ni due to its higher fraction of lighter protons. Hence, elements heavier than iron require a
supernova A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a powerful and luminous stellar explosion. This transient astronomical event occurs during the last stellar evolution, evolutionary stages of a massive star or when a ...

supernova
for their formation, involving by starting 56Fe nuclei. In the far future of the universe, assuming that
proton decay #REDIRECT Proton decay #REDIRECT Proton decay#REDIRECT Proton decay In particle physics Particle physics (also known as high energy physics) is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epi ...

proton decay
does not occur, cold occurring via
quantum tunnelling Quantum tunnelling or tunneling (US) is the quantum mechanical Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The proce ...
would cause the light nuclei in ordinary matter to fuse into 56Fe nuclei. Fission and would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron.


Origin and occurrence in nature


Cosmogenesis

Iron's abundance in
rocky planets A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun ...
like Earth is due to its abundant production during the runaway fusion and explosion of type Ia supernovae, which scatters the iron into space.


Metallic iron

Metallic or
native iron{{infobox mineral , name = Iron, native iron or telluric iron , boxwidth = , boxbgcolor = , image = Iron-136213.jpg , imagesize = 260px , alt = , caption = Sawed slab of basalt with bright, metallic native iro ...
is rarely found on the surface of the Earth because it tends to oxidize. However, both the Earth's inner and
outer core Earth's outer core is a fluid layer about thick and composed of mostly iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transi ...
, that account for 35% of the mass of the whole Earth, are believed to consist largely of an iron alloy, possibly with
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
. Electric currents in the liquid outer core are believed to be the origin of the
Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. Fo ...
. The other
terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Su ...
s (
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
,
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...
, and
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...
) as well as the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
are believed to have a metallic core consisting mostly of iron. The
M-type asteroid Definition M-type (aka M-class) asteroids are a Asteroid spectral types, spectral class of asteroids which appear to contain higher concentrations of metal phases (e.g. iron-nickel) than other asteroid classes, and are widely thought to be the s ...
s are also believed to be partly or mostly made of metallic iron alloy. The rare
iron meteorite Iron meteorites, also known as siderite :''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known ...
s are the main form of natural metallic iron on the Earth's surface. Items made of cold-worked meteoritic iron have been found in various archaeological sites dating from a time when iron smelting had not yet been developed; and the
Inuit Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples Indigenous peoples, also referred to as First people, Aboriginal people, Native people, or autochthonous people, ...
in
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an autonomous territory An autonomous administrative division (also referred to as an autonomous area, entity, unit, region, subdivision, or territory) is a subnational administra ...

Greenland
have been reported to use iron from the
Cape York meteorite The Cape York meteorite, also known as the Innaanganeq meteorite, is one of the largest known iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel a ...
for tools and hunting weapons. About 1 in 20
meteorite A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces ...
s consist of the unique iron-nickel minerals
taenite 200px, Widmanstätten pattern showing the two forms of Nickel-Iron, Kamacite and Taenite, in an octahedrite meteorite Taenite (Fe, Ni) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-log ...
(35–80% iron) and
kamacite Kamacite is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...
(90–95% iron). Native iron is also rarely found in basalts that have formed from magmas that have come into contact with carbon-rich sedimentary rocks, which have reduced the oxygen
fugacity In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas w ...
sufficiently for iron to crystallize. This is known as
Telluric iron{{infobox mineral , name = Iron, native iron or telluric iron , boxwidth = , boxbgcolor = , image = Iron-136213.jpg , imagesize = 260px , alt = , caption = Sawed slab of basalt with bright, metallic native iro ...
and is described from a few localities, such as
Disko Island Disko Island ( kl, Qeqertarsuaq, da, Diskoøen) is a large island in Baffin Bay, off the west coast of Greenland. It has an area of ,
in West Greenland,
Yakutia Sakha, also known as Yakutia or Yakutiya,; sah, Саха Сирэ, r= Saqa Sire, p= saˈxa sɪrjə), and officially known as the Republic of Sakha (Yakutia) ( rus, Республика Саха (Якутия), r= Respublika Sakha (Yakutiya), p ...

Yakutia
in Russia and Bühl in Germany.


Mantle minerals

FerropericlaseFerropericlase or magnesiowüstite Wüstite (Fe O) is a mineral form 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.https://www.mindat.org/min-4316.htmlhtt ...
, a solid solution of
periclase Periclase is a magnesium Magnesium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of at ...
(MgO) and
wüstite Wüstite (FeO) is a mineral form 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.https://www.mindat.org/min-4316.htmlhttps://www.ima-mineralogy.org/Minlis ...
(FeO), makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after
silicate perovskite Silicate perovskite is either (Mg,Fe)SiO3 (the magnesium end-member is called bridgmanite) or CaSiO3 (calcium silicate Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·Si ...
; it also is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction γ- transforms γ-olivine into a mixture of silicate perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite.Ferropericlase
Mindat.org
Silicate perovskite Silicate perovskite is either (Mg,Fe)SiO3 (the magnesium end-member is called bridgmanite) or CaSiO3 (calcium silicate Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·Si ...
may form up to 93% of the lower mantle, and the magnesium iron form, , is considered to be the most abundant
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. (2 ...

mineral
in the Earth, making up 38% of its volume.


Earth's crust

While iron is the most abundant element on Earth, most of this iron is concentrated in the inner and outer cores. The fraction of iron that is in
Earth's crust Earth's crust is a thin shell on the outside of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The ...
only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
, and
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
). Most of the iron in the crust is combined with various other elements to form many
iron minerals Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is Abundance ...
. An important class is the
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
minerals such as
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
(Fe2O3),
magnetite Magnetite is a 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 for ...

magnetite
(Fe3O4), and
siderite :''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of ...

siderite
(FeCO3), which are the major ores of iron. Many
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock i ...
s also contain the sulfide minerals
pyrrhotite Pyrrhotite is an iron sulfide mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks ...

pyrrhotite
and
pentlandite Pentlandite is an iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the period ...
.Klein, Cornelis and Cornelius S. Hurlbut, Jr. (1985) ''Manual of Mineralogy,'' Wiley, 20th ed, pp. 278–79 During
weathering Weathering is the deterioration of Rock (geology), 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 o ...
, iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
.Greenwood and Earnshaw, p. 1071 Large deposits of iron are banded iron formations, a type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor
shale Shale is a fine-grained, clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defi ...

shale
and
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a preci ...

chert
. The banded iron formations were laid down in the time between and . Materials containing finely ground iron(III) oxides or oxide-hydroxides, such as
ochre Ochre ( ; from grc, ὤχρα, from , , pale), or ocher in American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the ...
, have been used as yellow, red, and brown
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 compound , CH4; is among the simplest organic compou ...
s since pre-historical times. They contribute as well to the color of various rocks and
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
s, including entire geological formations like the in
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

Oregon
and the
Buntsandstein The Buntsandstein (German for ''coloured'' or ''colourful sandstone'') or Bunter sandstone is a lithostratigraphic and allostratigraphic unit (a sequence of rock strata) in the Subsurface (geology), subsurface of large parts of west and central E ...

Buntsandstein
("colored sandstone", British Bunter). Through ''Eisensandstein'' (a
jurassic The Jurassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
'iron sandstone', e.g. from
Donzdorf Donzdorf is a town in the Göppingen (district), district of Göppingen in Baden-Württemberg in southern Germany. It is located 12 km east of Göppingen, and 13 km south of Schwäbisch Gmünd. The town is home to Nuclear Blast Records, ...
in Germany) and Bath stone in the UK, iron compounds are responsible for the yellowish color of many historical buildings and sculptures. The proverbial red color of the surface of Mars is derived from an iron oxide-rich
regolith Regolith () is a blanket of unconsolidated, loose, Homogeneity and heterogeneity, heterogeneous superficial deposits covering solid Rock (geology), rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moo ...

regolith
. Significant amounts of iron occur in the iron sulfide mineral
pyrite The 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. R ...

pyrite
(FeS2), but it is difficult to extract iron from it and it is therefore not exploited. In fact, iron is so common that production generally focuses only on ores with very high quantities of it. According to the
International Resource Panel The International Resource Panel is a scientific panel of experts that aims to help nations use natural resources , Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States ...
's Metal Stocks in Society report, the global stock of iron in use in society is 2,200 kg per capita. More-developed countries differ in this respect from less-developed countries (7,000–14,000 vs 2,000 kg per capita).


Oceans

Ocean science demonstrated the role of the iron in the ancient seas in both marine biota and climate.


Chemistry and compounds

Iron shows the characteristic chemical properties of the
transition metal In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations tha ...
s, namely the ability to form variable oxidation states differing by steps of one and a very large coordination and organometallic chemistry: indeed, it was the discovery of an iron compound,
ferrocene Ferrocene is an organometallic chemistry, organometallic compound with the formula . The molecule is a Cyclopentadienyl complex, complex consisting of two Cyclopentadienyl anion, cyclopentadienyl rings bound to a central iron atom. It is an oran ...

ferrocene
, that revolutionalized the latter field in the 1950s.Greenwood and Earnshaw, p. 905 Iron is sometimes considered as a prototype for the entire block of transition metals, due to its abundance and the immense role it has played in the technological progress of humanity. Its 26 electrons are arranged in the
configuration Configuration or configurations may refer to: Computing * Computer configuration or system configuration * Configuration file, a software file used to configure the initial settings for a computer program * Configurator, also known as choice board, ...
d64s2, of which the 3d and 4s electrons are relatively close in energy, and thus it can lose a variable number of electrons and there is no clear point where further ionization becomes unprofitable. Iron forms compounds mainly in the
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge ...
s +2 (
iron(II) In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
, "ferrous") and +3 ( iron(III), "ferric"). Iron also occurs in higher oxidation states, e.g. the purple (K2FeO4), which contains iron in its +6 oxidation state. Although iron(VIII) oxide (FeO4) has been claimed, the report could not be reproduced and such a species from the removal of all electrons of the element beyond the preceding inert gas configuration (at least with iron in its +8 oxidation state) has been found to be improbable computationally. However, one form of anionic [FeO4] with iron in its +7 oxidation state, along with an iron(V)-peroxo isomer, has been detected by infrared spectroscopy at 4 K after cocondensation of laser-ablated Fe atoms with a mixture of O2/Ar. Iron(IV) is a common intermediate in many biochemical oxidation reactions. Numerous organoiron chemistry, organoiron compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy. Many mixed valence compounds contain both iron(II) and iron(III) centers, such as
magnetite Magnetite is a 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 for ...

magnetite
and
Prussian blue Prussian blue (also known as Berlin blue or, in painting Painting is the practice of applying paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, ...

Prussian blue
(). The latter is used as the traditional "blue" in blueprints. Iron is the first of the transition metals that cannot reach its group oxidation state of +8, although its heavier congeners ruthenium and osmium can, with ruthenium having more difficulty than osmium. Ruthenium exhibits an aqueous cationic chemistry in its low oxidation states similar to that of iron, but osmium does not, favoring high oxidation states in which it forms anionic complexes. In the second half of the 3d transition series, vertical similarities down the groups compete with the horizontal similarities of iron with its neighbors
cobalt Cobalt is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

cobalt
and
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
in the periodic table, which are also ferromagnetic at room temperature and share similar chemistry. As such, iron, cobalt, and nickel are sometimes grouped together as the iron triad.Greenwood and Earnshaw, p. 1070 Unlike many other metals, iron does not form amalgams with mercury (element), mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron. Iron is by far the most reactive element in its group; it is pyrophoric when finely divided and dissolves easily in dilute acids, giving Fe2+. However, it does not react with concentrated nitric acid and other oxidizing acids due to the formation of an impervious oxide layer, which can nevertheless react with hydrochloric acid. High purity iron, called electrolytic iron, is considered to be resistant to rust, due to its oxide layer.


Binary compounds


Oxides and hydroxides

Iron forms various iron oxide, oxide and hydroxide compounds; the most common are iron(II,III) oxide (Fe3O4), and
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
(Fe2O3). Iron(II) oxide also exists, though it is unstable at room temperature. Despite their names, they are actually all non-stoichiometric compounds whose compositions may vary. These oxides are the principal ores for the production of iron (see bloomery and blast furnace). They are also used in the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS2), also known as fool's gold owing to its golden luster. It is not an iron(IV) compound, but is actually an iron(II) polysulfide containing Fe2+ and ions in a distorted sodium chloride structure.Greenwood and Earnshaw, p. 1079


Halides

The binary ferrous and ferric halides are well-known. The ferrous halides typically arise from treating iron metal with the corresponding hydrohalic acid to give the corresponding hydrated salts. :Fe + 2 HX → FeX2 + H2 (X = F, Cl, Br, I) Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common. :2 Fe + 3 X2 → 2 FeX3 (X = F, Cl, Br) Ferric iodide is an exception, being thermodynamically unstable due to the oxidizing power of Fe3+ and the high reducing power of I: :2 I + 2 Fe3+ → I2 + 2 Fe2+ (E0 = +0.23 V) Ferric iodide, a black solid, is not stable in ordinary conditions, but can be prepared through the reaction of iron pentacarbonyl with iodine and carbon monoxide in the presence of hexane and light at the temperature of −20 °C, with oxygen and water excluded. Complexes of ferric iodide with some soft bases are known to be stable compounds.


Solution chemistry

The standard reduction potentials in acidic aqueous solution for some common iron ions are given below:Greenwood and Earnshaw, pp. 1075–79 The red-purple tetrahedral ferrate(VI) anion is such a strong oxidizing agent that it oxidizes nitrogen and ammonia at room temperature, and even water itself in acidic or neutral solutions:Greenwood and Earnshaw, pp. 1082–84 :4 + 10 → 4 + 20 + 3 O2 The Fe3+ ion has a large simple cationic chemistry, although the pale-violet hexaquo ion is very readily hydrolyzed when pH increases above 0 as follows:Greenwood and Earnshaw, pp. 1088–91 As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
precipitates out of solution. Although Fe3+ has a d5 configuration, its absorption spectrum is not like that of Mn2+ with its weak, spin-forbidden d–d bands, because Fe3+ has higher positive charge and is more polarizing, lowering the energy of its ligand-to-metal charge-transfer complex, charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region. On the other hand, the pale green iron(II) hexaquo ion does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises quickly in air to form
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
that accounts for the brown deposits present in a sizeable number of streams.Greenwood and Earnshaw, pp. 1091–97


Coordination compounds

Due to its electronic structure, iron has a very large coordination and organometallic chemistry. Many coordination compounds of iron are known. A typical six-coordinate anion is hexachloroferrate(III), [FeCl6]3−, found in the mixed salt (chemistry), salt tetrakis(methylammonium) hexachloroferrate(III) chloride. Complexes with multiple bidentate ligands have geometric isomers. For example, the ''trans''-chlorohydridobis(bis-1,2-(diphenylphosphino)ethane)iron(II) complex is used as a starting material for compounds with the moiety (chemistry), moiety. The ferrioxalate ion with three oxalate ligands (shown at right) displays helical chirality with its two non-superposable geometries labelled ''Λ'' (lambda) for the left-handed screw axis and ''Δ'' (delta) for the right-handed screw axis, in line with IUPAC conventions. Potassium ferrioxalate is used in chemical actinometry and along with its sodium ferrioxalate, sodium salt undergoes photoreduction applied in old-style photographic processes. The hydrate, dihydrate of iron(II) oxalate has a polymeric structure with co-planar oxalate ions bridging between iron centres with the water of crystallisation located forming the caps of each octahedron, as illustrated below. Iron(III) complexes are quite similar to those of
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
(III) with the exception of iron(III)'s preference for ''O''-donor instead of ''N''-donor ligands. The latter tend to be rather more unstable than iron(II) complexes and often dissociate in water. Many Fe–O complexes show intense colors and are used as tests for phenols or enols. For example, in the ferric chloride test, used to determine the presence of phenols, iron(III) chloride reacts with a phenol to form a deep violet complex: :3 ArOH + FeCl3 → Fe(OAr)3 + 3 HCl (Ar = aryl) Among the halide and pseudohalide complexes, fluoro complexes of iron(III) are the most stable, with the colorless [FeF5(H2O)]2− being the most stable in aqueous solution. Chloro complexes are less stable and favor tetrahedral coordination as in [FeCl4]; [FeBr4] and [FeI4] are reduced easily to iron(II). Thiocyanate is a common test for the presence of iron(III) as it forms the blood-red [Fe(SCN)(H2O)5]2+. Like manganese(II), most iron(III) complexes are high-spin, the exceptions being those with ligands that are high in the spectrochemical series such as cyanide. An example of a low-spin iron(III) complex is [Fe(CN)6]3−. The cyanide ligands may easily be detached in [Fe(CN)6]3−, and hence this complex is poisonous, unlike the iron(II) complex [Fe(CN)6]4− found in Prussian blue, which does not release hydrogen cyanide except when dilute acids are added. Iron shows a great variety of electronic spin states (d electrons), spin states, including every possible spin quantum number value for a d-block element from 0 (diamagnetic) to (5 unpaired electrons). This value is always half the number of unpaired electrons. Complexes with zero to two unpaired electrons are considered low-spin and those with four or five are considered high-spin. Iron(II) complexes are less stable than iron(III) complexes but the preference for ''O''-donor ligands is less marked, so that for example is known while is not. They have a tendency to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used.


Organometallic compounds

Organoiron chemistry is the study of organometallic compounds of iron, where carbon atoms are covalently bound to the metal atom. They are many and varied, including cyanometallate, cyanide complexes, carbonyl complexes, sandwich compound, sandwich and half-sandwich compounds.
Prussian blue Prussian blue (also known as Berlin blue or, in painting Painting is the practice of applying paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, ...

Prussian blue
or "ferric ferrocyanide", Fe4[Fe(CN)6]3, is an old and well-known iron-cyanide complex, extensively used as pigment and in several other applications. Its formation can be used as a simple wet chemistry test to distinguish between aqueous solutions of Fe2+ and Fe3+ as they react (respectively) with potassium ferricyanide and potassium ferrocyanide to form Prussian blue. Another old example of an organoiron compound is iron pentacarbonyl, Fe(CO)5, in which a neutral iron atom is bound to the carbon atoms of five carbon monoxide molecules. The compound can be used to make carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives triiron dodecacarbonyl, , a complex with a cluster of three iron atoms at its core. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state. A landmark in this field was the discovery in 1951 of the remarkably stable sandwich compound
ferrocene Ferrocene is an organometallic chemistry, organometallic compound with the formula . The molecule is a Cyclopentadienyl complex, complex consisting of two Cyclopentadienyl anion, cyclopentadienyl rings bound to a central iron atom. It is an oran ...

ferrocene
, by Peter L. Paulson, Paulson and T. J.Kealy, Kealy and independently by S. A. Miller, Miller and others, whose surprising molecular structure was determined only a year later by Robert Burns Woodward, Woodward and Geoffrey Wilkinson, Wilkinson and Ernst Otto Fischer, Fischer. Ferrocene is still one of the most important tools and models in this class.Greenwood and Earnshaw, p. 1104 Iron-centered organometallic species are used as catalysts. The Knölker complex, for example, is a transfer hydrogenation catalyst for ketones.


Industrial uses

The iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7Water of crystallization, H2O) and iron(III) chloride (FeCl3). The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt (). Iron(II) compounds tend to be oxidized to iron(III) compounds in the air.


Etymology

As iron has been in use for such a long time, it has many names. The source of its chemical symbol ''Fe'' is the Latin word ''ferrum'', and its descendants are the names of the element in the Romance languages (for example, French language, French ''fer'', Spanish language, Spanish ''hierro'', and Italian language, Italian and Portuguese language, Portuguese ''ferro''). The word ''ferrum'' itself possibly comes from the Semitic languages, via Etruscan language, Etruscan, from a root that also gave rise to Old English language, Old English ''bræs'' "brass". The English word ''iron'' derives ultimately from Proto-Germanic language, Proto-Germanic ''*isarnan'', which is also the source of the German name ''Eisen'' and Dutch ''ijzeren''. It was most likely borrowed from Celtic languages, Celtic ''*isarnon'', which ultimately comes from Proto-Indo-European "powerful, holy" and finally "strong", referencing iron's strength as a metal. Kluge relates ''*isarnon'' to Illyric and Latin ''Wrath, ira'', 'wrath'). The Balto-Slavic language, Balto-Slavic names for iron (e.g. Russian language, Russian железо [''zhelezo''], Polish language, Polish ''żelazo'', Lithuanian language, Lithuanian ''geležis'') are the only ones to come directly from the Proto-Indo-European ''*ghelgh-'' "iron". In many of these languages, the word for ''iron'' may also be used to denote other objects made of iron or steel, or figuratively because of the hardness and strength of the metal. The Chinese language, Chinese ''tiě'' (traditional Chinese, traditional 鐵; simplified Chinese, simplified 铁) derives from Proto-Sino-Tibetan language, Proto-Sino-Tibetan ''*hliek'', and was borrowed into Japanese language, Japanese as 鉄 ''tetsu'', which also has the native reading ''kurogane'' "black metal" (similar to how iron is referenced in the English word blacksmith).


History


Development of iron metallurgy

Iron is one of the elements undoubtedly known to the ancient world. It has been worked, or wrought iron, wrought, for millennia. However, iron objects of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes. The technology developed slowly, and even after the discovery of smelting it took many centuries for iron to replace bronze as the metal of choice for tools and weapons.


Meteoritic iron

Beads made from meteoric iron in 3500 BC or earlier were found in Gerzeh culture, Gerzeh, Egypt by G.A. Wainwright. The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities. Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools. For example, a Tutankhamun's iron dagger blade, dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite discovered in the area, deposited by an ancient meteor shower. Items that were likely made of iron by Egyptians date from 3000 to 2500 BC. Meteoritic iron is comparably soft and ductile and easily cold forging, cold forged but may get brittle when heated because of the
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
content.


Wrought iron

The first iron production started in the Middle Bronze Age, but it took several centuries before iron displaced bronze. Samples of smelting, smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700 BC. The Hittites established an empire in north-central Anatolia around 1600 BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society. The Hittites began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC. The subsequent period is called the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history Human history, or world history, is the narrative of Human, humanity's pa ...
. Artifacts of smelted iron are found in History of metallurgy in the Indian subcontinent, India dating from 1800 to 1200 BC, and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus). Alleged references (compare history of metallurgy in South Asia) to iron in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term ''ayas'' (metal) refers to copper, while iron which is called as ''śyāma ayas'', literally "black copper", first is mentioned in the post-rigvedic Atharvaveda. Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC. Iron working was introduced to Ancient Greece, Greece in the late 11th century BC, from which it spread quickly throughout Europe. The spread of ironworking in Central and Western Europe is associated with Celts, Celtic expansion. According to Pliny the Elder, iron use was common in the Ancient Rome, Roman era. In the lands of what is now considered China, iron appears approximately 700–500 BC. Iron smelting may have been introduced into China through Central Asia.Pigott, Vincent C. (1999). ''The Archaeometallurgy of the Asian Old World''. Philadelphia: University of Pennsylvania Museum of Archaeology and Anthropology. , p. 8. The earliest evidence of the use of a blast furnace in China dates to the 1st century AD, and cupola furnaces were used as early as the Warring States period (403–221 BC).Pigott, Vincent C. (1999). ''The Archaeometallurgy of the Asian Old World''. Philadelphia: University of Pennsylvania Museum of Archaeology and Anthropology. , p. 191. Usage of the blast and cupola furnace remained widespread during the Song dynasty, Song and Tang dynasty, Tang Dynasties. During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the Puddling (metallurgy), puddling process for refining iron ore. It was later improved by others, including Joseph Hall (metallurgist), Joseph Hall.


Cast iron

Cast iron was first produced in China during 5th century BC, but was hardly in Europe until the medieval period. The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel. Medieval blast furnaces were about tall and made of fireproof brick; forced air was usually provided by hand-operated bellows. Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times. In 1709, Abraham Darby I established a Coke (fuel), coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century. Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative The Iron Bridge, first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines.Greenwood and Earnshaw, p. 1072 Railways have been central to the formation of modernity and ideas of progress and various languages (e.g. French, Spanish, Italian and German) refer to railways as ''iron road''.


Steel

Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making good steel by 1000 BC. Then improved versions, Wootz steel by India and Damascus steel were developed around 300 BC and AD 500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities.


Foundations of modern chemistry

In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one.


Symbolic role

Iron plays a certain role in mythology and has found various usage Iron (metaphor), as a metaphor and in Iron in folklore, folklore. The Greeks, Greek poet Hesiod's ''Works and Days'' (lines 109–201) lists different ages of man named after metals like gold, silver, bronze and iron to account for successive ages of humanity. The Iron Age was closely related with Rome, and in Ovid's ''Metamorphoses'' An example of the importance of iron's symbolic role may be found in the German Campaign of 1813. Frederick William III commissioned then the first Iron Cross as military decoration. Berlin iron jewellery reached its peak production between 1813 and 1815, when the Prussian royal family urged citizens to donate gold and silver jewellery for military funding. The inscription ''Gold gab ich für Eisen'' (I gave gold for iron) was used as well in later war efforts.



Laboratory routes

For a few limited purposes when it is needed, pure iron is produced in the laboratory in small quantities by reducing the pure oxide or hydroxide with hydrogen, or forming iron pentacarbonyl and heating it to 250 °C so that it decomposes to form pure iron powder. Another method is electrolysis of ferrous chloride onto an iron cathode.


Main industrial route

Nowadays, the industrial production of iron or steel consists of two main stages. In the first stage, iron ore is redox, reduced with coke (fuel), coke in a blast furnace, and the molten metal is separated from gross impurities such as silicate minerals. This stage yields an alloy—pig iron—that contains relatively large amounts of carbon. In the second stage, the amount of carbon in the pig iron is lowered by oxidation to yield wrought iron, steel, or cast iron.Greenwood and Earnshaw, p. 1073 Other metals can be added at this stage to form alloy steels.


Blast furnace processing

The blast furnace is loaded with iron ores, usually
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
or
magnetite Magnetite is a 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 for ...

magnetite
, together with coke (coal that has been separately baked to remove volatile components). Air pre-heated to 900 °C is blown through the mixture, in sufficient amount to turn the carbon into carbon monoxide: :2 C + O2 → 2 CO This reaction raises the temperature to about 2000 °C. The carbon monoxide reduces the iron ore to metallic iron :Fe2O3 + 3 CO → 2 Fe + 3 CO2 Some iron in the high-temperature lower region of the furnace reacts directly with the coke: :2 Fe2O3 + 3 C → 4 Fe + 3 CO2 A flux (metallurgy), flux such as limestone (calcium carbonate) or Dolomite (mineral), dolomite (calcium-magnesium carbonate) is also added to the furnace's load. Its purpose is to remove silicaceous minerals in the ore, which would otherwise clog the furnace. The heat of the furnace decomposes the carbonates to calcium oxide, which reacts with any excess silica to form a slag composed of calcium silicate or other products. At the furnace's temperature, the metal and the slag are both molten. They collect at the bottom as two immiscible liquid layers (with the slag on top), that are then easily separated. The slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.


Steelmaking

The pig iron produced by the blast furnace process contains up to 4–5% carbon (by mass), with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. This high level of carbon makes it relatively weak and brittle. Reducing the amount of carbon to 0.002–2.1% produces
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appe ...

steel
, which may be up to 1000 times harder than pure iron. A great variety of steel articles can then be made by cold working, hot rolling, forging, machining, etc. Removing the impurities from pig iron, but leaving 2–4% carbon, results in
cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impuritie ...
, which is cast by foundry, foundries into articles such as stoves, pipes, radiators, lamp-posts, and rails. Steel products often undergo various heat treatments after they are forged to shape. annealing (metallurgy), Annealing consists of heating them to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable.Verhoeven, J.D. (1975) ''Fundamentals of Physical Metallurgy'', Wiley, New York, p. 326


Direct iron reduction

Owing to environmental concerns, alternative methods of processing iron have been developed. "Direct reduced iron, Direct iron reduction" Sponge iron reaction, reduces iron ore to a ferrous lump called sponge iron, "sponge" iron or "direct" iron that is suitable for steelmaking. Two main reactions comprise the direct reduction process: Natural gas is partially oxidized (with heat and a catalyst): :2 CH4 + O2 → 2 CO + 4 H2 Iron ore is then treated with these gases in a furnace, producing solid sponge iron: :Fe2O3 + CO + 2 H2 → 2 Fe + CO2 + 2 H2O Silica is removed by adding a limestone flux as described above.


Thermite process

Ignition of a mixture of aluminium powder and iron oxide yields metallic iron via the thermite reaction: :Fe2O3 + 2 Al → 2 Fe + Al2O3 Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, Puddling (metallurgy), puddling furnaces, Bessemer converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.


Applications


As structural material

Iron is the most widely used of all the metals, accounting for over 90% of worldwide metal production. Its low cost and high strength often make it the material of choice material to withstand stress or transmit forces, such as the construction of machinery and machine tools, track (rail transport), rails, automobiles, hull (ship), ship hulls, rebar, concrete reinforcing bars, and the load-carrying framework of buildings. Since pure iron is quite soft, it is most commonly combined with alloying elements to make steel.Greenwood and Earnshaw, pp. 1070–71


Mechanical properties

The mechanical properties of iron and its alloys are extremely relevant to their structural applications. Those properties can be evaluated in various ways, including the Brinell scale, Brinell test, the Rockwell scale, Rockwell test and the Vickers hardness test. The properties of pure iron are often used to calibrate measurements or to compare tests. However, the mechanical properties of iron are significantly affected by the sample's purity: pure, single crystals of iron are actually softer than aluminium, and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell. The pure iron (99.9 %~99.999 %), especially called electrolytic iron, is industrially produced by Electrolytic process, electrolytic refining. An increase in the carbon content will cause a significant increase in the hardness and tensile strength of iron. Maximum hardness of Rockwell scale, 65 Rc is achieved with a 0.6% carbon content, although the alloy has low tensile strength. Because of the softness of iron, it is much easier to work with than its heavier Congener (chemistry), congeners
ruthenium Ruthenium is a chemical element with the Symbol (chemistry), symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to ...

ruthenium
and
osmium Osmium (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximat ...

osmium
.Greenwood and Earnshaw, pp. 1074–75


Types of steels and alloys

α-Iron is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C). Austenite (γ-iron) is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
used for making cutlery, and hospital and food-service equipment. Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel. The reduction of contaminants in pig iron that negatively affect material properties, such as sulfur and phosphorus, yields cast iron containing 2–4% carbon, 1–6% silicon, and small amounts of
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
. Pig iron has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly and depend on the form the carbon takes in the alloy. "White" cast irons contain their carbon in the form of cementite, or iron carbide (Fe3C). This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken iron carbide, a very pale, silvery, shiny material, hence the appellation. Cooling a mixture of iron with 0.8% carbon slowly below 723 °C to room temperature results in separate, alternating layers of cementite and α-iron, which is soft and malleable and is called pearlite for its appearance. Rapid cooling, on the other hand, does not allow time for this separation and creates hard and brittle martensite. The steel can then be tempered by reheating to a temperature in between, changing the proportions of pearlite and martensite. The end product below 0.8% carbon content is a pearlite-αFe mixture, and that above 0.8% carbon content is a pearlite-cementite mixture. In gray iron the carbon exists as separate, fine flakes of graphite, and also renders the material brittle due to the sharp edged flakes of graphite that produce stress concentration sites within the material. A newer variant of gray iron, referred to as ductile iron, is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, reducing the stress concentrations and vastly increasing the toughness and strength of the material. Wrought iron contains less than 0.25% carbon but large amounts of slag that give it a fibrous characteristic. It is a tough, malleable product, but not as fusible as pig iron. If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped within the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing. Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less, with small amounts of
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as
chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

chromium
, vanadium, molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA steel, HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost. Alloys with high purity elemental makeups (such as alloys of electrolytic iron) have specifically enhanced properties such as ductility, tensile strength, toughness, fatigue limit, fatigue strength, heat resistance, and corrosion resistance. Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation as a function of energy is shown in the graph. The main disadvantage of iron and steel is that pure iron, and most of its alloys, suffer badly from
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous ferric oxides, hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxi ...

rust
if not protected in some way, a cost amounting to over 1% of the world's economy. Painting, galvanization, Passivation (chemistry), passivation, plastic coating and bluing (steel), bluing are all used to protect iron from rust by excluding
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
and oxygen or by cathodic protection. The mechanism of the rusting of iron is as follows:Greenwood and Earnshaw, p. 1076 :Cathode: 3 O2 + 6 H2O + 12 e → 12 OH :Anode: 4 Fe → 4 Fe2+ + 8 e; 4 Fe2+ → 4 Fe3+ + 4 e :Overall: 4 Fe + 3 O2 + 6 H2O → 4 Fe3+ + 12 OH → 4 Fe(OH)3 or 4 FeO(OH) + 4 H2O The electrolyte is usually iron(II) sulfate in urban areas (formed when atmospheric sulfur dioxide attacks iron), and salt particles in the atmosphere in seaside areas.


Iron compounds

Although the dominant use of iron is in metallurgy, iron compounds are also pervasive in industry. Iron catalysts are traditionally used in the Haber–Bosch process for the production of ammonia and the Fischer–Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricants. Powdered iron in an acidic solvent was used in the Bechamp reduction the reduction of nitrobenzene to aniline. Iron based catalysts play a crucial role in converting biobased raw materials into valuable bulk - and fine chemicals, in fuel cells as well as in removal of hazardous chemicals. Iron(III) oxide mixed with
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
powder can be ignited to create a thermite, thermite reaction, used in welding large iron parts (like railroad, rails) and purifying ores. Iron(III) oxide and Iron(III) oxyhidroxide, oxyhidroxide are used as reddish and ocher
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 compound , CH4; is among the simplest organic compou ...
s. Iron(III) chloride finds use in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an industrial etching, etchant for
copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

copper
in the manufacture of printed circuit boards. It can also be dissolved in alcohol to form tincture of iron, which is used as a medicine to stop bleeding in Domestic canary, canaries. Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to redox, reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesis.


Biological and pathological role

Iron is required for life. The iron–sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Iron-containing proteins participate in transport, storage and used of oxygen. Iron proteins are involved in electron transfer. Examples of iron-containing proteins in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase. The average adult human contains about 0.005% body weight of iron, or about four grams, of which three quarters is in hemoglobin – a level that remains constant despite only about one milligram of iron being absorbed each day, because the human body recycles its hemoglobin for the iron content. Microbial growth may be assisted by oxidation of iron(II) or by reduction of iron (III).


Biochemistry

Iron acquisition poses a problem for aerobic organisms because ferric iron is poorly soluble near neutral pH. Thus, these organisms have developed means to absorb iron as complexes, sometimes taking up ferrous iron before oxidising it back to ferric iron. In particular, bacteria have evolved very high-affinity wikt:sequester, sequestering agents called siderophores. After uptake in human cell (biology), cells, iron storage is precisely regulated. A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the bloodstream, blood to cells. Transferrin contains Fe3+ in the middle of a distorted octahedron, bonded to one nitrogen, three oxygens and a chelating carbonate anion that traps the Fe3+ ion: it has such a high Stability constants of complexes, stability constant that it is very effective at taking up Fe3+ ions even from the most stable complexes. At the bone marrow, transferrin is reduced from Fe3+ and Fe2+ and stored as ferritin to be incorporated into hemoglobin. The most commonly known and studied bioinorganic chemistry, bioinorganic iron compounds (biological iron molecules) are the heme proteins: examples are
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
,
myoglobin Myoglobin (symbol Mb or MB) is an iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their ...

myoglobin
, and cytochrome P450. These compounds participate in transporting gases, building
enzymes Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...
, and transferring electrons.Greenwood and Earnshaw, pp. 1098–104 Metalloproteins are a group of proteins with metal ion cofactor (biochemistry), cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP. Hemoglobin is an oxygen carrier that occurs in red blood cells and contributes their color, transporting oxygen in the arteries from the lungs to the muscles where it is transferred to
myoglobin Myoglobin (symbol Mb or MB) is an iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their ...

myoglobin
, which stores it until it is needed for the metabolic oxidation of glucose, generating energy. Here the hemoglobin binds to carbon dioxide, produced when glucose is oxidized, which is transported through the veins by hemoglobin (predominantly as bicarbonate anions) back to the lungs where it is exhaled. In hemoglobin, the iron is in one of four heme groups and has six possible coordination sites; four are occupied by nitrogen atoms in a porphyrin ring, the fifth by an imidazole nitrogen in a histidine residue of one of the protein chains attached to the heme group, and the sixth is reserved for the oxygen molecule it can reversibly bind to. When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe2+ ion at the center of the heme group (in the hydrophobic protein interior) is in a Spin states (d electrons)#High-spin and low-spin systems, high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe2+ ion about 55 picometers above it. In this configuration, the sixth coordination site reserved for the oxygen is blocked by another histidine residue. When deoxyhemoglobin picks up an oxygen molecule, this histidine residue moves away and returns once the oxygen is securely attached to form a hydrogen bond with it. This results in the Fe2+ ion switching to a low-spin configuration, resulting in a 20% decrease in ionic radius so that now it can fit into the porphyrin ring, which becomes planar. (Additionally, this hydrogen bonding results in the tilting of the oxygen molecule, resulting in a Fe–O–O bond angle of around 120° that avoids the formation of Fe–O–Fe or Fe–O2–Fe bridges that would lead to electron transfer, the oxidation of Fe2+ to Fe3+, and the destruction of hemoglobin.) This results in a movement of all the protein chains that leads to the other subunits of hemoglobin changing shape to a form with larger oxygen affinity. Thus, when deoxyhemoglobin takes up oxygen, its affinity for more oxygen increases, and vice versa. Myoglobin, on the other hand, contains only one heme group and hence this cooperative effect cannot occur. Thus, while hemoglobin is almost saturated with oxygen in the high partial pressures of oxygen found in the lungs, its affinity for oxygen is much lower than that of myoglobin, which oxygenates even at low partial pressures of oxygen found in muscle tissue. As described by the Bohr effect (named after Christian Bohr, the father of Niels Bohr), the oxygen affinity of hemoglobin diminishes in the presence of carbon dioxide. Carbon monoxide and phosphorus trifluoride are poisonous to humans because they bind to hemoglobin similarly to oxygen, but with much more strength, so that oxygen can no longer be transported throughout the body. Hemoglobin bound to carbon monoxide is known as carboxyhemoglobin. This effect also plays a minor role in the toxicity of cyanide, but there the major effect is by far its interference with the proper functioning of the electron transport protein cytochrome a. The cytochrome proteins also involve heme groups and are involved in the metabolic oxidation of glucose by oxygen. The sixth coordination site is then occupied by either another imidazole nitrogen or a methionine sulfur, so that these proteins are largely inert to oxygen – with the exception of cytochrome a, which bonds directly to oxygen and thus is very easily poisoned by cyanide. Here, the electron transfer takes place as the iron remains in low spin but changes between the +2 and +3 oxidation states. Since the reduction potential of each step is slightly greater than the previous one, the energy is released step-by-step and can thus be stored in adenosine triphosphate. Cytochrome a is slightly distinct, as it occurs at the mitochondrial membrane, binds directly to oxygen, and transports protons as well as electrons, as follows: :4 Cytc2+ + O2 + 8H → 4 Cytc3+ + 2 H2O + 4H Although the heme proteins are the most important class of iron-containing proteins, the iron-sulfur proteins are also very important, being involved in electron transfer, which is possible since iron can exist stably in either the +2 or +3 oxidation states. These have one, two, four, or eight iron atoms that are each approximately tetrahedrally coordinated to four sulfur atoms; because of this tetrahedral coordination, they always have high-spin iron. The simplest of such compounds is rubredoxin, which has only one iron atom coordinated to four sulfur atoms from cysteine residues in the surrounding peptide chains. Another important class of iron-sulfur proteins is the ferredoxins, which have multiple iron atoms. Transferrin does not belong to either of these classes. The ability of sea mussels to maintain their grip on rocks in the ocean is facilitated by their use of organometallic chemistry, organometallic iron-based bonds in their protein-rich cuticles. Based on synthetic replicas, the presence of iron in these structures increased elastic modulus 770 times, tensile strength 58 times, and toughness 92 times. The amount of stress required to permanently damage them increased 76 times.


Nutrition


Diet

Iron is pervasive, but particularly rich sources of dietary iron include red meat, oysters, lentils, beans, poultry, fish, leaf vegetables, watercress, tofu, chickpeas, black-eyed peas, and blackstrap molasses. Bread and breakfast cereals are sometimes specifically fortified with iron. Iron provided by dietary supplements is often found as iron(II) fumarate, although iron(II) sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one-third to two-thirds the efficiency (relative to iron sulfate), is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when Chelation, chelated to amino acids and is also available for use as a common iron supplement. Glycine, the least expensive amino acid, is most often used to produce iron glycinate supplements.


Dietary recommendations

The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iron in 2001. The current EAR for iron for women ages 14–18 is 7.9 mg/day, 8.1 for ages 19–50 and 5.0 thereafter (post menopause). For men the EAR is 6.0 mg/day for ages 19 and up. The RDA is 15.0 mg/day for women ages 15–18, 18.0 for 19–50 and 8.0 thereafter. For men, 8.0 mg/day for ages 19 and up. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 27 mg/day and, for lactation, 9 mg/day. For children ages 1–3 years 7 mg/day, 10 for ages 4–8 and 8 for ages 9–13. As for safety, the IOM also sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of iron the UL is set at 45 mg/day. Collectively the EARs, RDAs and ULs are referred to as Dietary Reference Intakes. The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women the PRI is 13 mg/day ages 15–17 years, 16 mg/day for women ages 18 and up who are premenopausal and 11 mg/day postmenopausal. For pregnancy and lactation, 16 mg/day. For men the PRI is 11 mg/day ages 15 and older. For children ages 1 to 14 the PRI increases from 7 to 11 mg/day. The PRIs are higher than the U.S. RDAs, with the exception of pregnancy. The EFSA reviewed the same safety question did not establish a UL. Infants may require iron supplements if they are bottle-fed cow's milk. Frequent Blood donation, blood donors are at risk of low iron levels and are often advised to supplement their iron intake. For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For iron labeling purposes 100% of the Daily Value was 18 mg, and remained unchanged at 18 mg. A table of the old and new adult daily values is provided at Reference Daily Intake.


Deficiency

Iron deficiency is the most common nutritional deficiency in the world. When loss of iron is not adequately compensated by adequate dietary iron intake, a state of latent iron deficiency occurs, which over time leads to iron-deficiency anemia if left untreated, which is characterised by an insufficient number of red blood cells and an insufficient amount of hemoglobin. Children, pre-menopausal women (women of child-bearing age), and people with poor diet are most susceptible to the disease. Most cases of iron-deficiency anemia are mild, but if not treated can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.


Excess

Human iron metabolism, Iron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron. Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is primarily accomplished by regulating uptake. Regulation of iron uptake is impaired in some people as a result of a Genetic disorder, genetic defect that maps to the HLA-H gene region on chromosome 6 and leads to abnormally low levels of hepcidin, a key regulator of the entry of iron into the circulatory system in mammals. In these people, excessive iron intake can result in iron overload disorders, known medically as hemochromatosis. Many people have an undiagnosed genetic susceptibility to iron overload, and are not aware of a family history of the problem. For this reason, people should not take iron supplements unless they suffer from iron deficiency (medicine), iron deficiency and have consulted a doctor. Hemochromatosis is estimated to be the cause of 0.3 to 0.8% of all metabolic diseases of Caucasians. Overdoses of ingested iron can cause excessive levels of free iron in the blood. High blood levels of free ferrous iron react with peroxides to produce highly reactive free radicals that can damage DNA, proteins, lipids, and other cellular components. Iron toxicity occurs when the cell contains free iron, which generally occurs when iron levels exceed the availability of transferrin to bind the iron. Damage to the cells of the Human gastrointestinal tract, gastrointestinal tract can also prevent them from regulating iron absorption, leading to further increases in blood levels. Iron typically damages cells in the heart, liver and elsewhere, causing adverse effects that include coma, metabolic acidosis, Shock (circulatory), shock, liver failure, coagulopathy, adult respiratory distress syndrome, long-term organ damage, and even death. Humans experience iron toxicity when the iron exceeds 20 milligrams for every kilogram of body mass; 60 milligrams per kilogram is considered a lethal dose. Overconsumption of iron, often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological causes of death in children under six. The Dietary Reference Intake (DRI) sets the Tolerable Upper Intake Level (UL) for adults at 45 mg/day. For children under fourteen years old the UL is 40 mg/day. The medical management of iron toxicity is complicated, and can include use of a specific chelation, chelating agent called deferoxamine to bind and expel excess iron from the body.


ADHD

Some research has suggested that low thalamic iron levels may play a role in the pathophysiology of ADHD. Some researchers have found that iron supplementation can be effective especially in the inattentive subtype of the disorder. Further, research has shown that iron has the potential to decrease the risk of cardiovascular events during treatment with ADHD drugs or can be used as an intervention to optimize response to psychostimulants at a lower dose.


Cancer

The role of iron in cancer defense can be described as a "double-edged sword" because of its pervasive presence in non-pathological processes. People having chemotherapy may develop iron deficiency and anemia, for which intravenous iron therapy is used to restore iron levels. Iron overload, which may occur from high consumption of red meat, may initiate tumor growth and increase susceptibility to cancer onset, particularly for colorectal cancer.


Marine systems

Iron plays an essential role in marine systems and can act as a limiting nutrient for planktonic activity. Because of this, too much of a decrease in iron may lead to a decrease in growth rates in phytoplanktonic organisms such as diatoms. Iron can also be oxidized by marine microbes under conditions that are high in iron and low in oxygen. Iron can enter marine systems through adjoining rivers and directly from the atmosphere. Once iron enters the ocean, it can be distributed throughout the water column through ocean mixing and through recycling on the cellular level. In the arctic, sea ice plays a major role in the store and distribution of iron in the ocean, depleting oceanic iron as it freezes in the winter and releasing it back into the water when thawing occurs in the summer. The iron cycle can fluctuate the forms of iron from aqueous to particle forms altering the availability of iron to primary producers. Increased light and warmth increases the amount of iron that is in forms that are usable by primary producers.Tagliabue, A., Bopp, L., Aumont,O., & Arrigo, K.R. (2009). Influence of light and temperature on the marine iron cycle: From theoretical to global modeling. Global Biogeochemical Cycles, 23.


See also

* El Mutún in Bolivia, where 10% of the world's accessible iron ore is located * Iron and steel industry * Iron cycle * Iron nanoparticle * Iron–platinum nanoparticle * Iron fertilization – proposed fertilization of oceans to stimulate phytoplankton growth * Iron-oxidizing bacteria * List of countries by iron production * Pelletizing, Pelletising – process of creation of iron ore pellets * Rustproof iron * Steel


References


Bibliography

* *


Further reading

* H.R. Schubert, ''History of the British Iron and Steel Industry ... to 1775 AD'' (Routledge, London, 1957) * R.F. Tylecote, ''History of Metallurgy'' (Institute of Materials, London 1992). * R.F. Tylecote, "Iron in the Industrial Revolution" in J. Day and R.F. Tylecote, ''The Industrial Revolution in Metals'' (Institute of Materials 1991), 200–60.


External links


It's Elemental – Iron


at ''The Periodic Table of Videos'' (University of Nottingham)
Metallurgy for the non-Metallurgist


by J.B. Calvert {{good article Iron, Chemical elements Transition metals Ferromagnetic materials Biology and pharmacology of chemical elements Dietary minerals Cubic minerals Minerals in space group 225 Minerals in space group 229 Building materials Pyrotechnic fuels Chemical elements with body-centered cubic structure Native element minerals