mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal System: Amorphous; Streak: Yellowish-brown; Specific Gravity: 2.7-4.3

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

Identified April 1, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal System: Amorphous; Streak: Yellowish-brown; Specific Gravity: 2.7-4.3

Formation & geological history

Formed in the oxidation zones of iron-bearing mineral deposits and as a secondary mineral in sedimentary rocks involving the weathering of minerals like siderite, magnetite, and pyrite.

Uses & applications

Historically used as an important iron ore and as a source of yellow pigment (ochre). Currently used in specimen collecting and as a secondary iron source.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It was the source of 'yellow ochre' used by prehistoric humans for cave paintings.

Field identification & locations

Identify by its distinctive yellowish-brown streak on a porcelain plate and its earthy appearance. Commonly found in boggy areas (bog iron) or as a coating on other rocks in oxidized zones.