mineral

Limonite (Iron Ore)

FeO(OH)nH2O

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

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

Identified May 4, 2026More mineral →

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Physical properties

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

Formation & geological history

Secondary mineral formed by the oxidation of iron-rich mineral deposits (like pyrite) in the weathering zone. Frequently found in marshy settings as 'bog iron'.

Uses & applications

Historically used as an important iron ore; currently used as a pigment (yellow ochre) in paints and dyes.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, 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 yellow-brown streak (even if the rock looks dark) and lack of magnetism compared to magnetite. Found in sedimentary environments and gossans.