sedimentary

Limonite (Iron Ore)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form distinct crystals); Specific Gravity: 2.7 to 4.3.

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

Identified April 5, 2026More sedimentary →

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Physical properties

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (does not form distinct crystals); Specific Gravity: 2.7 to 4.3.

Formation & geological history

Formed from the secondary alteration of other iron minerals through weathering and oxidation in oxidizing environments. It is often found as a precipitate in swamps (bog iron) or as a capping over iron-bearing hydrothermal deposits.

Uses & applications

Historically used as a major source of iron ore; currently used as a pigment (yellow ochre) in dyes and paints and as an additive in cement manufacturing.

Geological facts

Limonite is not a true mineral, but a mixture of related hydrated iron oxide minerals, primarily goethite. It was one of the earliest pigments used by humans, found in prehistoric cave paintings.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak and earthy appearance. It often appears as a rusty coating on other rocks. Commonly found in gossans (iron hats) and bog deposits globally.