sedimentary

Ironstone Concretion

Iron oxide-cemented sedimentary concretion

AI-generated identification · may be incorrect

Hardness of 5-6 on the Mohs scale, brownish-orange to reddish-brown exterior with a greyish core, dull luster, amorphous or cryptocrystalline structure, no distinct cleavage, specific gravity around 3.0-4.0.

Identified November 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of iron oxide minerals around a nucleus within sedimentary layers, typically in shallow marine or freshwater environments during the Paleozoic or Mesozoic eras.

Uses & applications

Primarily of interest to rockhounds and fossil collectors; historically used as a minor ore of iron and sometimes polished for decorative purposes.

Geological facts

These nodules are frequently mistaken for meteorites or fossils due to their unusual rounded shapes. They often form around ancient plant fragments or shells.

Field identification & locations

Easily identified by their distinctive rusty exterior, layered cross-section, and heavy weight relative to size. Commonly found in sedimentary rock formations worldwide, particularly in shale and sandstone beds.