mineral
Limonite with Ironstone
Limonite (hydrated iron(III) oxide-hydroxides), FeO(OH)·nH2O
Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (pseudomorphous); Specific Gravity: 2.7-4.3.
- Hardness
- 4-5
- Color
- Yellowish-brown to dark brown
- Luster
- Dull or earthy
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Physical properties
Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (pseudomorphous); Specific Gravity: 2.7-4.3.
Formation & geological history
Formed as a secondary mineral through the oxidation and weathering of primary iron-bearing minerals like pyrite, magnetite, and siderite in the oxidation zone of ore deposits.
Uses & applications
A major source of iron ore historically; used as a natural earthy pigment (yellow ochre) in paints and coatings.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mainly goethite. It has been used as a pigment by humans for over 15,000 years, seen in prehistoric cave paintings.
Field identification & locations
Identify by its characteristic yellow-brown streak, earthy appearance, and lack of cleavage. Often found in bog deposits or as caps over iron-rich veins.
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