sedimentary

Ironstone concretion (possibly limonite/goethite-bearing)

Limonite, a mixture of hydrated iron oxides, commonly including goethite (α-FeO(OH))

AI-generated identification · may be incorrect

Small, irregular, dark brown to black specimen with rusty yellow-brown patches and a dull to locally shiny luster. Likely Mohs hardness about 4–5.5; exact composition and properties cannot be confirmed from the image.

Identified September 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Iron-rich minerals can precipitate or accumulate in sediments and weathering zones, forming ironstone concretions. Such deposits occur across many geological ages and environments.

Uses & applications

Ironstone is generally collected as a curiosity; iron-rich material has also been used as low-grade iron ore and pigment.

Geological facts

“Limonite” is a field term for a mixture of hydrated iron oxides rather than one mineral with a fixed formula.

Field identification & locations

Look for rusty brown or ochre staining, relatively high heft, and an earthy or botryoidal surface; these traits are not diagnostic, and a close examination or simple tests would help distinguish it from slag or other iron minerals. Ironstone is widespread in sedimentary rocks and weathered soils.