mineral

Limonite (Iron Ore)

Limonite (Iron oxide-hydroxide mixture, FeO(OH)·nH2O)

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (microcrystalline); Specific Gravity: 2.7 to 4.3.

Hardness: 4 to 5
Color: Yellowish-brown to dark brown
Luster: Dull to earthy

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (microcrystalline); Specific Gravity: 2.7 to 4.3.

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich mineral deposits (like pyrite or magnetite) or as a chemical precipitate in bog environments (bog iron). It is post-magmatic and found in sedimentary environments.

Uses & applications

Historically used as a major ore of iron; currently used primarily as a natural pigment (yellow ochre) in paints, dyes, and coatings.

Geological facts

Limonite is not a true mineral species but a mixture of hydrated iron oxide minerals, mostly goethite. It has been used as a pigment since prehistoric times, appearing in cave paintings worldwide.

Field identification & locations

Identify by its distinctive yellowish-brown (ochre) streak and earthy appearance. It is commonly found in the 'gossan' or iron cap sitting atop sulfur-rich ore deposits.

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