Goethite is a hydrated iron oxide, or iron oxyhydroxide, of chemical formula FeO(OH) (orthorhombic crystal system). Goethite forms by weathering of iron-rich minerals and it is commonly found in soils. It may also be precipitated by groundwater in low-temperature environments (authigenic goethite in marine and lacustrine sediments). Silica-associated goethite has been found in hydrothermal deposits. The occurrence of goethite on planetary surfaces could be used as an indicator of low-temperature weathering with the involvement of liquid water.