mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0 - 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (no visible crystals); Cleavage: None; Specific Gravity: 2.7 - 4.3

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

Identified April 11, 2026More mineral →

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Physical properties

Hardness: 4.0 - 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (no visible crystals); Cleavage: None; Specific Gravity: 2.7 - 4.3

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich mineral deposits (like pyrite or magnetite) in sedimentary environments. Common in bog iron and oxidized zones of ore deposits.

Uses & applications

Historically used as a major iron ore and as a source of yellow-brown ochre pigment for paints. Today it is mostly a collector's mineral or low-grade ore.

Geological facts

Limonite is not a true mineral species but a mixture of hydrated iron oxide minerals. It is the material that gives many soils their yellow or brown color.

Field identification & locations

Identify by its characteristic yellowish-brown streak and earthy, 'rusty' appearance. Found worldwide in areas with heavy groundwater leaching. Look for it in weathered rock outcrops or near iron mines.