sedimentary

Limonite Concretion

Goethite-rich Concretion (FeO(OH))

AI-generated identification · may be incorrect

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Structure: Amorphous/Microcrystalline; Opaque with a centered cavity.

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

Identified May 19, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Structure: Amorphous/Microcrystalline; Opaque with a centered cavity.

Formation & geological history

Formed by the precipitation of iron oxide minerals from groundwater within sedimentary rock layers, often around a host nucleus or through the weathering of iron-rich minerals. Common in Mesozoic and Cenozoic age sediments.

Uses & applications

Primarily of interest to collectors and educators as a curiosity; historically used as a low-grade iron ore (limonite).

Geological facts

These are sometimes called 'rattle stones' (Klapperstein) if the internal core is loose and makes noise when shaken. They are common in iron-rich sandstone formations.

Field identification & locations

Identify by the rusty yellow-brown color, heavy iron weight relative to size, and hollow or multi-layered 'onion' structure. Frequently found in stream beds or eroded hillsides.