mineral
Limonite or Goethite (Ironstone)
Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs), Color: Dark brown to earthy yellow/orange, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5 (Mohs), Color: Dark brown to earthy yellow/orange, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None
Formation & geological history
Formed as secondary mineral species through the oxidation and weathering of primary iron-bearing minerals (like pyrite or magnetite) in sedimentary or metamorphic settings.
Uses & applications
Historically used as an iron ore and as a source for yellow and brown ochre pigments. In modern times, it is a minor ore of iron and a specimen for collectors.
Geological facts
Limonite is not a single mineral but a mixture of hydrated iron oxides, primarily goethite. It was the primary source of iron for many early human civilizations due to its abundance near the surface.
Field identification & locations
Identified by its signature yellowish-brown streak on a porcelain plate and its rusty appearance. Often found in wetlands (bog iron) or as a weathering crust on iron-rich rocks.
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