Ironstone is a sedimentary rock composed mainly of iron oxides, including hematite and goethite. It forms as a result of the precipitation of iron-rich minerals from groundwater or other iron-rich fluids. Ironstone is typically found in iron-rich sedimentary basins or in the vicinity of iron-rich volcanic rocks.
Ironstone is a valuable resource for the production of iron and steel, as it is a source of iron ore. The iron in ironstone is usually present as magnetite, hematite, or goethite. The iron content in ironstone varies from less than 20% to more than 60% by weight.
Ironstone formations are often associated with banded iron formations (BIFs), which are sedimentary rocks composed of alternating iron-rich and silica-rich layers. BIFs are found in many parts of the world, including Australia, Brazil, Canada, and South Africa.
Ironstone formations are also often associated with iron-rich sedimentary basins, such as the Bilbao Basin in Spain and the Iron Quadrangle in Brazil. These basins formed during the Mesozoic and Paleozoic eras and contain large deposits of iron ore.
In summary, ironstone is a sedimentary rock composed of iron oxides and is a source of iron ore. It is often associated with iron-rich sedimentary basins and banded iron formations, and is found in many parts of the world.