sedimentary

Ironstone concretion (likely limonite/goethite-rich)

Iron-oxide/hydroxide-cemented sediment, chiefly goethite (α-FeO(OH)) and limonite; exact identification requires testing

AI-generated identification · may be incorrect

Earthy brown, ochre and rusty-orange surface with irregular nodular form in a gravelly matrix. Goethite has Mohs hardness 5–5.5, submetallic to earthy luster and no prominent cleavage; the specimen’s crystal structure and density cannot be determined from the image.

Identified October 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as iron-rich groundwater precipitated oxides and hydroxides that cemented sediment into a concretion. Such deposits form in many geological periods and settings; age is not determinable visually.

Uses & applications

Usually collected as a geological curiosity or used as low-grade iron ore where deposits are sufficiently rich; this specimen appears mainly decorative or educational.

Geological facts

Iron oxides produce the characteristic rusty colors, while concretions can develop rounded, irregular shapes around a nucleus within sediment.

Field identification & locations

Look for dense, rusty-brown nodules, earthy coatings, and iron staining; a streak test and laboratory analysis can help distinguish goethite/limonite from other iron minerals. Ironstone occurs worldwide in sedimentary and weathering environments.