- Related Topics:
- oolitic iron deposit
- delta iron
- ferric iron compound
- gamma iron
- beta iron
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- Engineering LibreTexts - Iron (Oct. 16, 2026)
iron
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What is iron?
Iron (Fe) is a chemical element and a metal, ranking as the most abundant and cheapest metal in widespread use. It is the primary component of steel and is found in various minerals, notably hematite and magnetite. Iron constitutes about 5% of Earth's crust and is the most abundant element in Earth as a whole. In its pure form, iron is relatively soft, but its properties are significantly altered by the addition of carbon, forming steel. Iron has a melting point of 1,538 °C (2,800 °F).
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What are some everyday uses of iron?
Iron, a fundamental chemical element, is integral to numerous everyday applications due to its strength and versatility. It is the primary component of steel, which is extensively used in construction for buildings, bridges, and infrastructure. In transportation, iron and steel are crucial for manufacturing vehicles, trains, and ships. Everyday tools, from kitchen utensils to industrial machinery, are often made from iron or its alloys. Furthermore, iron is vital for household appliances, cookware, and even decorative items like railings and gates. Its magnetic properties also find use in various electronic components.
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Where is iron found in nature?
Iron is found in Earth's crust, making up about 5 percent of its composition, and is the fourth most abundant element overall. While the free metal is rare in the crust, iron is abundant in Earth's core, which is primarily composed of nickel-iron. Iron is also plentiful in the Sun and other stars.
In nature, iron is most commonly found combined with other elements in various minerals. The most significant iron ores are oxides, including hematite (Fe₂O₃), magnetite (Fe₃O₄), limonite (hydrated ferric oxide hydroxide), and siderite (FeCO₃). These ores are found in igneous, metamorphic, and sedimentary rocks. Major iron ore-producing countries include China, Brazil, Australia, Russia, and Ukraine.
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What are the main properties of iron as a metal?
Iron (Fe) is a dense metal with a silvery-white appearance and notable magnetic properties. It is the fourth most abundant element in Earth's crust and melts at 1,538° C (2,800° F). Iron is allotropic, meaning it exists in different crystal structures (body-centered cubic or face-centered cubic) depending on the temperature. In its pure form, iron is malleable, but it is typically used in alloys like steel to enhance its properties. Pure iron is reactive, especially in finely divided states, and readily combines with nonmetals. It is also ferromagnetic below 770° C (1,420° F), a property known as the Curie point.
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Why is iron important for living things?
Iron is crucial for living organisms, primarily for its role in oxygen transport and electron transfer reactions. In humans and many other animals, iron is a key component of hemoglobin, the protein in red blood cells responsible for carrying oxygen from the lungs to the body's tissues. Iron also functions as a cofactor for various enzymes, which are essential for catalyzing biochemical reactions necessary for life. Iron deficiency is a widespread nutritional deficiency, leading to conditions like iron-deficiency anemia, characterized by fatigue and reduced growth and development.
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How is iron extracted and processed from ore in industry?
Iron is primarily extracted from ore using a blast furnace, a process that releases iron from its chemical combination with oxygen. Iron ore, coke, and limestone are fed into the top of the furnace. Preheated air is blown in from the bottom, causing the coke to burn and generate intense heat. This heat reduces the iron oxides in the ore to metallic iron. The molten iron and slag collect at the bottom and are tapped off separately. Alternative methods like direct reduction and smelting reduction are also employed, though less common than the blast furnace.
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iron (Fe), chemical element, metal of Group 8 (VIIIb) of the periodic table, the most-used and cheapest metal.
| atomic number | 26 |
|---|---|
| atomic weight | 55.845 |
| melting point | 1,538 °C (2,800 °F) |
| boiling point | 3,000 °C (5,432 °F) |
| specific gravity | 7.86 (20 °C) |
| oxidation states | +2, +3, +4, +6 |
| electron configuration | [Ar]3d64s2 |
Occurrence, uses, and properties
Iron makes up 5 percent of Earth’s crust and is second in abundance to aluminum among the metals and fourth in abundance behind oxygen, silicon, and aluminum among the elements. Iron, which is the chief constituent of Earth’s core, is the most abundant element in Earth as a whole (about 35 percent) and is relatively plentiful in the Sun and other stars. In the crust the free metal is rare, occurring as terrestrial iron (alloyed with 2–3 percent nickel) in basaltic rocks in Greenland and carbonaceous sediments in the United States (Missouri) and as a low-nickel meteoric iron (5–7 percent nickel), kamacite. Nickel-iron, a native alloy, occurs in terrestrial deposits (21–64 percent iron, 77–34 percent nickel) and in meteorites as taenite (62–75 percent iron, 37–24 percent nickel). (For mineralogical properties of native iron and nickel-iron, see native elements [table].) Meteorites are classified as iron, iron-stone, or stony according to the relative proportion of their iron and silicate-mineral content. Iron is also found combined with other elements in hundreds of minerals; of greatest importance as iron ore are hematite (ferric oxide, Fe2O3), magnetite (triiron tetroxide, Fe3O4), limonite (hydrated ferric oxide hydroxide, FeO(OH)∙nH2O), and siderite (ferrous carbonate, FeCO3). Igneous rocks average about 5 percent iron content. The metal is extracted by smelting with carbon (coke) and limestone. (For specific information on the mining and production of iron, see iron processing.)
| country | mine production 2006 (metric tons)* | % of world mine production | demonstrated reserves 2006 (metric tons)*, ** | % of world demonstrated reserves |
|---|---|---|---|---|
| *Estimated. | ||||
| **Iron content. | ||||
| ***Detail does not add to total given because of rounding. | ||||
| Source: U.S. Department of the Interior, Mineral Commodity Summaries 2007. | ||||
| China | 520,000,000 | 30.8 | 15,000,000,000 | 8.3 |
| Brazil | 300,000,000 | 17.8 | 41,000,000,000 | 22.8 |
| Australia | 270,000,000 | 16.0 | 25,000,000,000 | 13.9 |
| India | 150,000,000 | 8.9 | 6,200,000,000 | 3.4 |
| Russia | 105,000,000 | 6.2 | 31,000,000,000 | 17.2 |
| Ukraine | 73,000,000 | 4.3 | 20,000,000,000 | 11.1 |
| United States | 54,000,000 | 3.2 | 4,600,000,000 | 2.6 |
| South Africa | 40,000,000 | 2.4 | 1,500,000,000 | 0.8 |
| Canada | 33,000,000 | 2.0 | 2,500,000,000 | 1.4 |
| Sweden | 24,000,000 | 1.4 | 5,000,000,000 | 2.8 |
| Iran | 20,000,000 | 1.2 | 1,500,000,000 | 0.8 |
| Venezuela | 20,000,000 | 1.2 | 3,600,000,000 | 2.0 |
| Kazakhstan | 15,000,000 | 0.9 | 7,400,000,000 | 4.1 |
| Mauritania | 11,000,000 | 0.7 | 1,000,000,000 | 0.6 |
| Mexico | 13,000,000 | 0.8 | 900,000,000 | 0.5 |
| other countries | 43,000,000 | 2.5 | 17,000,000,000 | 9.4 |
| world total | 1,690,000,000 | 100*** | 180,000,000,000 | 100*** |
The average quantity of iron in the human body is about 4.5 grams (about 0.004 percent), of which approximately 65 percent is in the form of hemoglobin, which transports molecular oxygen from the lungs throughout the body; 1 percent in the various enzymes that control intracellular oxidation; and most of the rest stored in the body (liver, spleen, bone marrow) for future conversion to hemoglobin. Red meat, egg yolk, carrots, fruit, whole wheat, and green vegetables contribute most of the 10–20 milligrams of iron required each day by the average adult. For the treatment of hypochromic anemias (caused by iron deficiency), any of a large number of organic or inorganic iron (usually ferrous) compounds are used.
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Iron, as commonly available, nearly always contains small amounts of carbon, which are picked up from the coke during smelting. These modify its properties, from hard and brittle cast irons containing up to 4 percent carbon to more malleable low-carbon steels containing less than 0.1 percent carbon.
Three true allotropes of iron in its pure form occur. Delta iron, characterized by a body-centred cubic crystal structure, is stable above a temperature of 1,390 °C (2,534 °F). Below this temperature there is a transition to gamma iron, which has a face-centred cubic (or cubic close-packed) structure and is paramagnetic (capable of being only weakly magnetized and only as long as the magnetizing field is present); its ability to form solid solutions with carbon is important in steelmaking. At 910 °C (1,670 °F) there is a transition to paramagnetic alpha iron, which is also body-centred cubic in structure. Below 773 °C (1,423 °F), alpha iron becomes ferromagnetic (i.e., capable of being permanently magnetized), indicating a change in electronic structure but no change in crystal structure. Above 773 °C (its Curie point), it loses its ferromagnetism altogether. Alpha iron is a soft, ductile, lustrous, gray-white metal of high tensile strength.
Pure iron is quite reactive. In a very finely divided state metallic iron is pyrophoric (i.e., it ignites spontaneously). It combines vigorously with chlorine on mild heating and also with a variety of other nonmetals, including all of the halogens, sulfur, phosphorus, boron, carbon, and silicon (the carbide and silicide phases play major roles in the technical metallurgy of iron). Metallic iron dissolves readily in dilute mineral acids. With nonoxidizing acids and in the absence of air, iron in the +2 oxidation state is obtained. With air present or when warm dilute nitric acid is used, some of the iron goes into solution as the Fe3+ ion. Very strongly oxidizing mediums—for example, concentrated nitric acid or acids containing dichromate—passivate iron (i.e., cause it to lose its normal chemical activity), however, much as they do chromium. Air-free water and dilute air-free hydroxides have little effect on the metal, but it is attacked by hot concentrated sodium hydroxide.
Natural iron is a mixture of four stable isotopes: iron-56 (91.66 percent), iron-54 (5.82 percent), iron-57 (2.19 percent), and iron-58 (0.33 percent).
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Iron compounds are amenable to study by taking advantage of a phenomenon known as the Mössbauer effect (the phenomenon of a gamma ray being absorbed and reradiated by a nucleus without recoil). Although the Mössbauer effect has been observed for about one-third of the elements, it is particularly for iron (and to a lesser extent tin) that the effect has been a major research tool for the chemist. In the case of iron the effect depends on the fact that the nucleus of iron-57 can be excited to a high energy state by the absorption of gamma radiation of very sharply defined frequency that is influenced by the oxidation state, electron configuration, and chemical environment of the iron atom and can thus be used as a probe of its chemical behavior. The marked Mössbauer effect of iron-57 has been used in studying magnetism and hemoglobin derivatives and for making a very precise nuclear clock.