mineral

Limonite (Iron Ore)

FeO(OH)·nH2O (Hydrous ferric oxide)

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form crystals); Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified March 1, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form crystals); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral in the oxidation zone of iron-rich mineral deposits; often produced by the weathering of pyrite, magnetite, or hematite. It is found in bog iron deposits and sedimentary rock layers.

Uses & applications

Historically used as an iron ore; currently used primarily as a pigment (yellow ochre) in paints, dyes, and coatings, and sometimes in geological collecting.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It is responsible for the 'rust' color in many soils and rock faces around the world.

Field identification & locations

Identified by its distinctive yellowish-brown streak on a porcelain plate and its earthy appearance. Commonly found in boggy areas or weathered rock outcrops. It is relatively heavy for its size due to iron content.

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