sedimentary

Weathered iron-rich concretion

Goethite–hematite limonite concretion, likely with quartz and clay minerals

AI-generated identification · may be incorrect

Typically brown to rusty orange, earthy to submetallic luster, irregular massive texture, and hardness about 4–6 Mohs depending on composition; no consistent cleavage, with moderate to high density. The surface shows weathering and possible botryoidal or concretionary textures.

Identified August 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when iron-bearing groundwater precipitated iron oxides and hydroxides around a nucleus in sediment, later hardened and weathered; commonly Cenozoic to Mesozoic, though concretions occur in rocks of many ages.

Uses & applications

Mostly a collector specimen; iron-rich material may historically serve as low-grade iron ore or natural pigment, but this piece has little industrial value.

Geological facts

Limonite is a field term for mixtures of hydrated iron oxides rather than a single mineral. Goethite and hematite commonly produce the yellow-brown to red-brown coloration.

Field identification & locations

Identify by its rusty color, heavy feel, earthy streak, and lack of visible crystalline structure; a reddish-brown to yellow streak on unglazed porcelain supports iron oxides. Common in sedimentary formations, soils, bogs, and weathered ore zones worldwide.