mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (microcrystalline); Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified May 29, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (microcrystalline); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral through the oxidation and hydration of iron-rich minerals (like pyrite) in the weathering zone of ore deposits and sedimentary environments.

Uses & applications

Historically used as a major iron ore; today used as a pigment (yellow ochre/umber) in paints, dyes, and coatings.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxides, primarily goethite. It has been used as a pigment by humans for over 30,000 years in cave paintings.

Field identification & locations

Identify by its characteristic yellowish-brown streak and earthy appearance. Found worldwide in gossans (weathered tops of ore veins) and bog deposits. Common in garden soil rocks.