sedimentary

Iron-rich concretion or ironstone nodule

Likely goethite- and/or hematite-cemented ironstone; exact identification requires testing

AI-generated identification · may be incorrect

Dark brown to gray, earthy to submetallic patches with a rough, irregular surface; likely Mohs hardness about 4–6, but composition and density cannot be determined reliably from the image. No obvious large crystals or cleavage are visible.

Identified September 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Iron oxides commonly precipitate from iron-bearing groundwater and cement sediment into nodules or concretions; such formations occur across many geological ages and settings.

Uses & applications

Ironstone has been used as iron ore and building stone; this small specimen is chiefly of interest to collectors.

Geological facts

A streak test can help distinguish iron oxides: hematite typically leaves a reddish-brown streak, while goethite often gives a yellow-brown streak.

Field identification & locations

The nodule-like shape and rusty brown areas suggest iron-rich material, but visual identification is uncertain; common ironstones occur in sedimentary rocks worldwide. A fresh streak, magnet test, and hardness test would help narrow it down.