sedimentary

Limonite Concretion

Limonite (Hydrated iron oxide) FeO(OH)·nH2O

AI-generated identification · may be incorrect

Hardness: 4.0-5.5; Color: Dark brown to yellowish-brown; Luster: Dull or earthy; Texture: Characterized by small circular pits or a botryoidal (grape-like) surface; Specific Gravity: 2.7-4.3.

Hardness: 4
Color: Dark brown to yellowish-brown
Luster: Dull or earthy

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 4.0-5.5; Color: Dark brown to yellowish-brown; Luster: Dull or earthy; Texture: Characterized by small circular pits or a botryoidal (grape-like) surface; Specific Gravity: 2.7-4.3.

Formation & geological history

Formed by the precipitation of iron oxides in sedimentary environments, often found in soil or rock cavities where groundwater has concentrated minerals over thousands to millions of years.

Uses & applications

Historically used as a low-grade iron ore (ochre); today primarily used as a pigment in paints and as mineral specimens for education.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, mostly goethite. The pitted appearance is often caused by the weathering of softer inclusions within the nodule.

Field identification & locations

Identify in the field by its high density relative to other stones and its rusty-brown streak when rubbed against tile. Often found in wetlands or areas with historic iron-rich runoff.