sedimentary

Limitation Concretion

Ironstone Concretion (Goethite/Limonite)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 (Mohs scale); Color: Ochre, rusty brown to tan; Luster: Dull/Earthy; Structure: Amorphous or microcrystalline; Cleavage: None (conchoidal fracture); Heavy for its size.

Hardness: 4
Color: Ochre, rusty brown to tan
Luster: Dull/Earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Ochre, rusty brown to tan; Luster: Dull/Earthy; Structure: Amorphous or microcrystalline; Cleavage: None (conchoidal fracture); Heavy for its size.

Formation & geological history

Formed by the precipitation of mineral cement, likely iron oxides, within the spaces between sediment grains. These often form in sedimentary rock layers like sandstone or shale during early diagenesis.

Uses & applications

Primarily collected as geological curiosities due to their unusual shapes; sometimes used as minor iron ore or crushed for pigments.

Geological facts

Concretions are often mistaken for fossils, bones, or meteorites due to their rounded, biological-looking shapes. The process of formation can take thousands to millions of years.

Field identification & locations

Identified by its heavy weight relative to its size and its distinct earthy, rusty color. Look for them in eroding cliffs, riverbeds, and sedimentary basins. If broken open, they sometimes reveal a target-like banding or a different core.