Goethite
Image: Didier Descouens (CC BY 4.0)
Mineral NameGoethite
Chemical FormulaFeO(OH)
Mohs Hardness5
Crystal Systemorthorhombic
Lusteradamantine
Streak Coloryellowish-brown
Cleavageperfect on {010}
Fractureuneven
Specific Gravity3.3
Colorsblack, dark brown, reddish-brown
Transparencyopaque
Type LocalityRestormel Royal Iron Mine (Trinity Mine), Lostwithiel, Lanivet Area, St Austell District, Cornwall, England, UK
Mineral GroupOxides
Usesiron ore, pigment, collector
Associated Mineralsquartz
Rarityuncommon
Description
The image shows numerous dark, lustrous, prismatic to acicular goethite crystals, some forming radiating aggregates, embedded within a matrix of white to translucent quartz, with some reddish staining.
Geological Context
Goethite is a common secondary mineral formed by the weathering of iron-rich minerals in oxidizing conditions, often found in gossans, bog iron ores, and as a component of limonite.
