mineral
Limonite (Yellow Ochre)
Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)
Hardness: 4-5.5; Color: Dull yellow to brownish; Luster: Earthy to sub-metallic; Crystal System: Amorphous/Microcrystalline; Cleavage: None; Opaque.
- Hardness
- 4-5
- Color
- Dull yellow to brownish
- Luster
- Earthy to sub-metallic
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Physical properties
Hardness: 4-5.5; Color: Dull yellow to brownish; Luster: Earthy to sub-metallic; Crystal System: Amorphous/Microcrystalline; Cleavage: None; Opaque.
Formation & geological history
Formed from the weathering and oxidation of iron-rich minerals such as pyrite, magnetite, and hematite in soil or marine environments. It is a secondary mineral found in oxidation zones of ore deposits.
Uses & applications
Historically used as a natural pigment (yellow ochre) for paints and dyes. It is also a minor ore of iron and used in the manufacturing of cement.
Geological facts
Limonite is not a single mineral but a mixture of related hydrated iron oxide minerals. It was one of the first pigments used by humans, as seen in prehistoric cave paintings.
Field identification & locations
Identified by its distinctive yellowish-brown streak and earthy appearance. Found worldwide in marshes, bogs, and as a surface coating on other rocks.
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