Goethite
Image: Robert M. Lavinsky (CC BY-SA 3.0)
Mineral NameGoethite
Chemical FormulaFeO(OH)
Mohs Hardness5.5
Crystal Systemorthorhombic
Lusteradamantine
Streak Coloryellowish-brown
Cleavageperfect on {010}
Fractureuneven
Specific Gravity3.3
Colorsdark brown, black, yellowish-brown, reddish-brown
Transparencyopaque
Type LocalityGraves Mountain, Lincoln County, Georgia, USA
Mineral GroupOxides
Usesminor iron ore, pigment, collector
Associated Mineralsquartz
Raritycommon
Description
This specimen features dark, almost black, botryoidal to acicular goethite crystals forming a crust or growth on translucent to white quartz crystals.
Geological Context
Goethite is a common secondary mineral formed by the weathering of iron-bearing minerals in various environments, including hydrothermal deposits, sedimentary settings, and as a component of lateritic soils. It is a major constituent of limonite.
