iron

Hard, malleable and ductile, silver-grey, metallic element, atomic number 26, relative atomic mass 55.847. It chemical symbol comes from the Latin ferrum. It is the fourth most abundant element in the Earth's crust. Iron occurs in concentrated deposits as the ores haematite (Fe₂O₃), spathic ore (FeCO₃), and magnetite (Fe₃O₄). It sometimes occurs as a free metal, occasionally as fragments of iron or iron–nickel meteorites.

Iron is extracted from iron ore in a blast furnace. The chemical reactions of iron with oxygen, water, acids, and other substances can be explained by its position in the middle of the reactivity series of metals. Iron is the most useful of all metals; it is strongly magnetic and is the basis for steel (an alloy with carbon and other elements) and cast iron. Steel is used for buildings, bridges, ships, car bodies, and tools. Stainless steel is used for car parts, kitchen sinks, and cutlery. In electrical equipment iron is used in permanent magnets and electromagnets, and forms the cores of transformers and magnetic amplifiers. The corrosion of iron is called rusting and is an example of an oxidation reaction. In the human body, iron is an essential component of haemoglobin, the molecule in red blood cells that transports oxygen to all parts of the body. A deficiency in the diet causes a form of anaemia.

Iron has been worked into tools by early peoples in both the Old World and the New and its use has persisted since the Iron Age of prehistory.

The central core of the Earth, the radius of which is believed to be 2,200 miles, is held to consist principally of iron with around 10% nickel. When the amounts in the crust and core are combined, iron is probably the most abundant constituent element of the planet.