sedimentary

Ironstone concretion (possibly pyrite-bearing)

Iron-rich sedimentary concretion, likely composed of goethite/limonite with possible pyrite

AI-generated identification · may be incorrect

Brown, rounded nodule with metallic-looking reflective patches. Likely hardness about 4–6 Mohs; iron oxides are earthy to submetallic, while pyrite is metallic and harder (6–6.5). The photo does not establish mineral identity or crystal structure.

Identified September 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Iron-rich minerals can cement sediment into concretions during diagenesis; pyrite may form in oxygen-poor sediment. Age and exact formation environment cannot be determined from the image.

Uses & applications

Mostly a collecting specimen; ironstone has been used as iron ore and, when suitable, as building stone.

Geological facts

Concretions often develop around a nucleus as minerals precipitate from groundwater, sometimes producing rounded forms and mixed mineral surfaces.

Field identification & locations

The rounded shape and brown iron-rich exterior fit ironstone, but reflective areas could be sulfides or other minerals. A streak test and examination of fresh surfaces can help; common occurrences include sedimentary formations worldwide.