sedimentary

Iron-rich concretion, likely limonite/goethite

Goethite (α-FeO(OH)) and/or limonite; exact identification requires testing

AI-generated identification · may be incorrect

Rusty brown to ochre, earthy to dull luster, irregular nodular texture, and no obvious crystal faces or cleavage. Goethite has Mohs hardness about 5–5.5; limonite is a variable mixture of hydrated iron oxides.

Identified October 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as iron-bearing minerals weathered and iron oxides accumulated or cemented sediment into a concretion. Such formations occur across many geological ages and settings.

Uses & applications

Iron oxides are ores and pigments; this small specimen is mainly suitable for a collection or display.

Geological facts

Limonite is a field term for mixtures of hydrated iron oxides rather than a single well-defined mineral species.

Field identification & locations

The knobby, rusty-brown surface suggests an iron-oxide concretion; a streak test may leave a yellow-brown to reddish-brown mark. Common in weathered soils, sedimentary rocks, and iron-rich deposits worldwide.