sedimentary

Ironstone Concretion

Ferruginous Concretion / Limonite-Goethite Aggregate

AI-generated identification · may be incorrect

Hardness varies from 4 to 5.5 on the Mohs scale, color ranges from yellowish-brown to dark reddish-brown, with a dull to submetallic luster. It features an amorphous crystal structure and lacks true cleavage.

Identified November 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the chemical precipitation of iron oxides and hydroxides around a nucleus within permeable sedimentary strata, typically during diagenesis.

Uses & applications

Primarily collected as a geological curiosity or lapidary material for tumbling and polishing into decorative display pieces.

Geological facts

These nodules often weather out of softer surrounding sandstone or shale due to their higher resistance to weathering, creating rugged, knobby shapes.

Field identification & locations

Identified by its heavy weight relative to size, rusty brown coloration, and irregular, pitted surface texture. Found globally in sedimentary environments.