goetite

Goetite is a mineral composed of hydrated iron oxyhydroxide, with the chemical formula FeO(OH). It is a member of the goethite group and is named after Johann Wolfgang von Goethe. Goetite is a common constituent of the Earth's crust and is found in various geological environments, often forming as a secondary mineral through the weathering of iron-bearing minerals. Its typical occurrence is in iron ore deposits, sedimentary rocks, and as a product of oxidation in soils and lateritic deposits.

The mineral is characterized by its reddish-brown to yellowish-brown color, with a streak that is typically yellowish-brown. Goetite has a Mohs hardness of 4 to 5 and a specific gravity of around 4.28. It crystallizes in the orthorhombic system, often appearing as prismatic crystals, acicular aggregates, or massive forms. It can also occur as botryoidal or stalactitic masses. Goetite is insoluble in water and most acids but can be dissolved in hot concentrated sulfuric acid.

Goetite plays a significant role in geochemistry, particularly in iron cycling and soil formation. It is a primary component of bog iron ore and is an important indicator mineral for paleoclimatic conditions. While not typically used as a primary ore of iron due to its relatively low iron content compared to hematite or magnetite, it can be a source of iron and is sometimes found in industrial mineral applications. Historically, goetite has also been used as a pigment.