mineral
Limonite (Ironstone) pseudomorph
Limonite (Hydrous ferric oxide), FeO(OH)·nH2O
Hardness: 4-5.5, Color: Brown to yellowish-brown, Luster: Dull or earthy, Crystal structure: Amorphous or microcrystalline, Specific gravity: 2.7-4.3
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5, Color: Brown to yellowish-brown, Luster: Dull or earthy, Crystal structure: Amorphous or microcrystalline, Specific gravity: 2.7-4.3
Formation & geological history
Formed primarily by the oxidation and hydration of iron-rich mineral ores (like pyrite) in the weathering zone of deposits. It often occurs as pseudomorphs where the limonite replaces the original crystal shape of another mineral.
Uses & applications
Historically used as an iron ore; currently used as a pigment (brown ochre) and as a collector specimen.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was the source of 'yellow ochre' used in prehistoric cave paintings.
Field identification & locations
Identified by its distinctive yellowish-brown streak on a porcelain plate and its density. Commonly found in gossans (weathered tops of ore veins) and sedimental bog deposits.
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