Iron is one of the most abundant and widely distributed elements in the earth’s crust, constituting more than 4% of the total. Its supply is essentially limitless in almost all regions of the world. However, because of its position or concentration in the earth’s crust, iron ore is not available to us, and much of it is in a form that cannot be used in current ironmaking practices.
Iron ore are rocks and minerals that can be heated and used to extract metallic iron in an economically feasible method. Both the iron and steel industries worldwide are reliant on iron ore as a primary source of iron. Iron ore minerals are mostly found as hematite and magnetite.
Australia and Brazil are among the world’s largest iron ore producers and hold a large portion of the world’s iron ore reserves. Brazil and Australia make up over half of the world's iron ore exports.
A large number of minerals contain iron; however, only a few are used commercially as sources of iron. Minerals containing important amounts of iron may be grouped according to their chemical compositions into oxides, carbonates, sulfides and silicates.
Magnetite has a chemical composition of Fe3O4, corresponding to 72.36% iron and 27.64% oxygen, has a color of dark gray to black, and a specific gravity from 5.16 to 5.18. It is strongly magnetic, so it will act as a natural magnet. The magnetic property of magnetite is important, as when oxidized, it can turn to hermatite (martite and limonite) but still maintaining its original crystalline form.
Hematite has a chemical composition of Fe2O3 corresponding to 69.94% iron and 30.06% oxygen, has a color from steel gray to dull red or bright red, and has a specific gravity of 5.26. Hematite is one of the most important iron minerals. It has a wide occurrence in many types of rocks and is of varying origins.
Limonite is the name commonly given to hydrous iron oxides that mineralogically are composed of various mixtures of the minerals goethite or lepidocrocite. The chemical formula for goethite is HFeO2 and that for lepidocrocite is FeO(OH). Goethite contains 62.85% iron, 27.01% oxygen, and 10.14% water; has a specific gravity in the range of 3.6–4.0, is commonly yellow or brown to nearly black in color.
Ilmenite has a chemical composition of FeTiO3, corresponding to 36.80% iron, 31.57% titanium, and 31.63% oxygen. This is commonly considered an iron titanate. Ilmenite is often associated in small amounts with magnetite. Although generally mined as a source of titanium rather than as an ore of iron, iron may be recovered as a byproduct.
Siderite has a chemical composition of FeCO3 corresponding to 48.20% iron, 37.99% CO2 and 13.81% oxygen, a specific gravity of 3.83–3.88, and a color from white to greenish gray and brown. Siderite commonly contains variable amounts of calcium, magnesium or manganese.
Maghemite has a chemical composition of β-Fe2O3, which is the transformation of Magnetite under secondary change effect of oxidation environment. The streak may be blown.