mineral

Limonite (Iron Ore)

FeO(OH)·nH2O

Hardness: 4-5.5 (Mohs scale), Color: Yellow-brown to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous (often pseudomorphous), Cleavage: None, Specific Gravity: 2.7-4.3

Hardness: 4-5

Identified June 13, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale), Color: Yellow-brown to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous (often pseudomorphous), Cleavage: None, Specific Gravity: 2.7-4.3

Formation & geological history

Formed by the oxidation and hydration of iron-rich minerals such as pyrite or magnetite in weathering zones of ore deposits. It is a secondary mineral commonly found in oxidised zones.

Uses & applications

Primary source of iron ore historically; used as a pigment (yellow ochre) in paints, ceramics, and construction.

Geological facts

Limonite isn't a single mineral but a mixture of hydrated iron oxide minerals. It was used as a pigment for thousands of years, including in prehistoric cave paintings.

Field identification & locations

Identified in the field by its distinct yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Often found in bog iron deposits or gossans above mineral veins.