sedimentary
Limonite/Goethite Concretion
Limonite (FeO(OH)nH2O) or Goethite (̑-FeO(OH))
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous or cryptic; Specific Gravity: 2.7-4.3
- Hardness
- 4
- Color
- Yellowish-brown to dark brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous or cryptic; Specific Gravity: 2.7-4.3
Formation & geological history
Formed through the oxidation and hydration of iron-rich minerals in sedimentary environments or as a secondary weathering product. These often form as concretions or bog iron.
Uses & applications
Historically used as an iron ore; currently used as a pigment (ochre) in paints and dyes, and for geological study.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It is the primary coloring agent in 'yellow ochre' paint used since prehistoric times.
Field identification & locations
Can be identified by its yellow-brown streak (when rubbed on unglazed porcelain) and earthy appearance. Highly common in weathered soil and sedimentary rock layers worldwide.
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