mineral
Limonite / Ironstone
Limonite (Hydrated Iron Oxide) - FeO(OH)·nH2O
Hardness: 4-5.5; Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellowish-brown to rusty orange
- Luster
- Dull, earthy
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Physical properties
Hardness: 4-5.5; Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed as a secondary mineral through the weathering and oxidation of iron-rich mineral deposits (like pyrite or magnetite) in sedimentary environments.
Uses & applications
Used historically as a source of iron ore and as a pigment (yellow ochre) in paints. Today it is mostly a collector specimen or industrial iron source.
Geological facts
Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, most commonly goethite. It is responsible for the yellow and brown colors in many soils.
Field identification & locations
Identify by its characteristic 'rust' color and yellowish-brown streak on a porcelain plate. Commonly found in bog deposits or as a staining on other rocks.
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