sedimentary

Limonite Concretion

Goethite/Limonite (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs scale), Color: Brownish-yellow to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous or cryptocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3

Hardness: 4-5

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5 (Mohs scale), Color: Brownish-yellow to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous or cryptocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3

Formation & geological history

Formed by the precipitation of iron oxide minerals from groundwater within sedimentary rock layers, often around a nucleus. They can range from the Cretaceous to the Holocene period.

Uses & applications

Primarily used as a minor ore of iron; also used as an ocher pigment and for educational geological collections.

Geological facts

Commonly known as 'bog iron' when found in marshes. Some hollow varieties are called 'rattle stones' because a smaller loose pebble may be trapped inside.

Field identification & locations

Identify by its heavy weight relative to size and yellowish-brown streak. Common in sandstone or clay-rich soil. Look for spherical or potato-like shapes with a distinct weathered rind.