sedimentary
Limonite with Iron Inclusions
Limonite (Hydrated Iron Oxide, FeO(OH)·nH2O)
Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to earthy brown; Luster: Dull, earthy, or submetallic; Crystal Structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.7-4.3.
- Hardness
- 4
- Color
- Yellowish-brown to earthy brown
- Luster
- Dull, earthy, or submetallic
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Physical properties
Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to earthy brown; Luster: Dull, earthy, or submetallic; Crystal Structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.7-4.3.
Formation & geological history
Formed by the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in secondary enrichment zones. Often found as bog iron or in weathered sedimentary ironstones.
Uses & applications
Historically used as a major iron ore. Today, it is primarily used as a pigment (yellow ochre) in paints, for manufacturing cement, and as a soil conditioner in agriculture.
Geological facts
Limonite is not a singular mineral but a mixture of hydrated iron oxide minerals, mainly goethite. It was used by many ancient cultures as the first source of iron and for cave paintings due to its bright earthy pigments.
Field identification & locations
Identify in the field by its distinct yellow-brown streak (even on black versions) and earthy odor when damp. Commonly found in riverbeds, marshy areas, and near oxidized ore veins. Collectors value it for 'pseudomorphs' where it replaces the shape of other minerals.
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