sedimentary

Limonite (Ironstone)

FeO(OH)·nH2O

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous/Microcrystalline, Specific Gravity: 2.7-4.3

Hardness: 4-5

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous/Microcrystalline, Specific Gravity: 2.7-4.3

Formation & geological history

Formed through the oxidation and hydration of iron-rich mineral deposits in sedimentary environments, often occurring as a weathered residue or bog iron.

Uses & applications

Historically used as a minor iron ore and as a source for yellow ochre pigment. Currently used for gravel in road construction or as mineral specimens.

Geological facts

Limonite is not a 'true mineral' but a mixture of hydrated iron oxide minerals, primarily goethite. It has been used as a pigment for cave paintings since prehistoric times.

Field identification & locations

Identify by its characteristic yellowish-brown streak and earthy appearance. Commonly found in gossans (weathered tops of ore veins) and swampy areas.