mineral/sedimentary

Limonite (Ironstone Concretion)

Limonite (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; Cleavage: None; Specific Gravity: 2.7 to 4.3.

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

Identified June 14, 2026More mineral/sedimentary →

Explore Limonite (Ironstone Concretion) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7 to 4.3.

Formation & geological history

Formed through the oxidation of iron-rich mineral deposits in sedimentary environments. Often found as nodules or concretions where iron precipitating from groundwater binds sediment together.

Uses & applications

Historically used as an iron ore and a source of yellow pigment (ochre). Currently utilized primarily in paint production and as mineral specimens for collectors.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was a primary source of iron for early civilizations and is the material that gives many desert sands and soils their reddish-yellow color.

Field identification & locations

Identify in the field by its characteristic 'rust-colored' streak and earthy appearance. Look for it in iron-rich sedimentary bands or as nodules in clay-rich soils. It is often found near swampy areas or gossans.