sedimentary

Iron-rich concretion or weathered ironstone

Goethite–hematite limonite aggregate; commonly described as limonite or ironstone

AI-generated identification · may be incorrect

Hardness about 4–6.5 Mohs, rusty brown to dark brown, earthy to submetallic luster, irregular botryoidal/concretionary texture, and no obvious cleavage. The porous cavities and strongly oxidized color are typical of hydrated iron oxides, though the image alone cannot confirm the exact mineral mix.

Identified August 12, 2026More sedimentary →

Explore Iron-rich concretion or weathered ironstone in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Likely formed when iron-bearing groundwater precipitated oxides and hydroxides around a nucleus or within sediment, followed by weathering and dehydration. Such material commonly forms in Cenozoic soils, weathering zones, bogs, and sedimentary deposits rather than as a single crystal.

Uses & applications

Used as iron ore when sufficiently rich, and occasionally as pigment or a display specimen; generally unsuitable for jewelry unless cut or polished.

Geological facts

Limonite is a field term for a mixture dominated by goethite and related hydrated iron oxides, not a single precisely defined mineral. A reddish-brown streak and attraction to a strong magnet may support an iron-rich identification.

Field identification & locations

Common in iron-rich soils and weathered rock worldwide; test streak on unglazed porcelain, density, and magnetism, while avoiding destructive tests on valuable specimens. It could also be a mineralized fossil or slag, so laboratory analysis would be needed for certainty.