mineral
Limonite (Ironstone)
FeO(OH)·nH2O (Hydrous ferric oxides)
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellowish-brown to dark brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed by the oxidation and hydration of iron-rich mineral ores (like pyrite or magnetite) through weathering. Common in soil horizons and Bog Iron deposits.
Uses & applications
Primary source of yellow ochre pigment for paints; historical source of iron ore for smelting; used in water filtration systems.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxides. It was used by prehistoric humans as one of the first cave-painting pigments.
Field identification & locations
Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusted appearance. Often found in swampy areas or gossans above ore bodies.
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Metamorphic
Epidote
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
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Mineral/Rock
Granite
Granite (Phaneritic intrusive igneous rock)
igneous