Goethite

Goethite (FeO(OH); /ˈɡɜːrtaɪt/) is an iron-bearing hydroxide mineral of the diaspore group. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment (brown ochre). Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).Iridescent goethite, Filón Sur Mine, Tharsis, Huelva, SpainGoethite from Minas Gerais, BrazilA sharp, disc-shaped calcite has here been completely replaced by goethite, which preserved the original form perfectlyGoethite coating/replacing rusted pyrite cubesFinely crystallized specimen of goethite from Lake George, Park County, Colorado, USA Goethite (FeO(OH); /ˈɡɜːrtaɪt/) is an iron-bearing hydroxide mineral of the diaspore group. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment (brown ochre). Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832). Goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore. Goethite's hardness ranges from 5.0 to 5.5 on the Mohs Scale, and its specific gravity varies from 3.3 to 4.3. The mineral forms prismatic needle-like crystals ('needle iron ore') but is more typically massive. Feroxyhyte and lepidocrocite are both polymorphs of the iron oxyhydroxide FeO(OH) which are stable at the pressure and temperature conditions of the Earth's surface. Although they have the same chemical formula as goethite, their different crystalline structures make them distinct minerals. Additionally, goethite has several high-pressure and high-temperature polymorphs, which may be relevant to the conditions of the Earth's interior. These include ε-FeOOH, which has an orthorhombic crystal structure, a cubic pyrite-type polymorph, and an ultradense hexagonal structure. Goethite often forms through the weathering of other iron-rich minerals, and thus is a common component of soils, concentrated in laterite soils. nanoparticulate authigenic goethite is a common diagenetic iron oxyhydroxide in both marine and lake sediments. The formation of goethite is marked by the oxidation state change of Fe2+ (ferrous) to Fe3+ (ferric), which allows for goethite to exist at surface conditions. Because of this oxidation state change, goethite is commonly seen as a pseudomorph. As iron-bearing minerals are brought to the zone of oxidation within the soil, the iron turns from iron(II) to iron(III), while the original shape of the parent mineral is retained. Examples of common goethite pseudomorphs are: goethites after pyrite, goethite, siderite, and marcasite, though any iron(II)-bearing mineral could become a goethite pseudomorph if proper conditions are met. It may also be precipitated by groundwater or in other sedimentary conditions, or form as a primary mineral in hydrothermal deposits. Goethite has also been found to be produced by the excretion processes of certain bacteria types. Goethite is found all over the planet, usually in the form of concretions, stalactitic formations, oolites (a form consisting of tiny round grains cemented together), reniform (kidney shapes) or botryoidal (globular, like bunches of grapes) accumulations. It is also a very common pseudomorph. It is frequently encountered in the swampy areas at the head of spring waters ('bog iron'), on cave floors, and on the bottom of lakes and small creeks. The boxworks or gossan resulting from the oxidation of sulfide ore deposits is formed of goethite along with other iron oxides and quartz. Significant deposits of goethite are found in England, Australia, Cuba, and Michigan, Minnesota, Missouri, Colorado, Alabama, Georgia, Virginia, and Tennessee, and Florida caves in the United States. Deposits significant in location, if not in abundance, have been found in the Martian crater Gusev by NASA's Spirit rover, providing strong evidence for the presence of liquid water on the planet in an earlier stage of its evolution. In 2015 it was reported that limpet's teeth have goethite fibres in them, which accounts for their extreme tensile strength.