mineral

Iron-rich concretion or weathered ironstone

Limonite/goethite-rich iron oxide aggregate, commonly approximated as FeO(OH)·nH₂O

AI-generated identification · may be incorrect

Brown to rusty brown, earthy to submetallic luster, irregular massive texture, and no visible crystal faces; hardness is typically 4–5.5 Mohs, with a yellow-brown streak and relatively high specific gravity (~3.3–4.3).

Identified August 31, 2026More mineral →

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Physical properties

Formation & geological history

Forms when iron-bearing minerals oxidize and hydrate during weathering, groundwater activity, or sediment cementation; its age depends on the host deposit and may range from recent to ancient. The image alone cannot distinguish a concretion from weathered ironstone or a fragment of iron-rich rock.

Uses & applications

Used historically as an iron ore and natural pigment; attractive pieces are mainly collected as curiosities. It has little jewelry or construction value unless part of a larger ironstone deposit.

Geological facts

A yellow-brown streak and attraction to a strong magnet can support an iron-rich identification, though limonite is often weakly magnetic. A reddish-brown powder and rusty interior are typical.

Field identification & locations

Common in soils, river gravels, sedimentary rocks, and weathered zones worldwide; test streak on unglazed porcelain, inspect a fresh break, and compare density and magnetism. Professional identification may require microscopy or X-ray diffraction.