Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, and has been mined for the production of iron since at least 400 BC.
Limonite
Bog iron ore
Limonite deposited from mine runoff
Galena and limonite
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe3O4, 72.4% Fe), hematite (Fe2O3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe), or siderite (FeCO3, 48.2% Fe).
Hematite, the main iron ore found in Brazilian mines
Stockpiles of iron ore pellets like this one are used in steel production.
An illustration of iron ore being unloaded at docks in Toledo, Ohio
Banded iron ock, estimated as being 2.1 billion years old