sedimentary

Weathered iron-rich concretion or ironstone nodule

Goethite–hematite limonite concretion (FeO(OH), Fe₂O₃, and hydrous iron oxides)

AI-generated identification · may be incorrect

Hardness is approximately 4–6 Mohs; brown to rusty red, earthy to dull/vitreous luster, massive and non-crystalline externally, with irregular botryoidal or pitted texture. It may leave a yellow-brown to reddish streak and feel relatively heavy for its size.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when groundwater precipitated iron oxides around a sedimentary nucleus, later weathering into a rounded concretion; age depends on its host sediment and cannot be determined visually. It commonly develops in soils, iron-rich sandstones, river gravels, and weathered rock.

Uses & applications

Used mainly as a specimen, pigment source, or iron ore when sufficiently concentrated; generally unsuitable for gemstones or structural construction.

Geological facts

The term “limonite” describes a mixture of hydrated iron oxides rather than one precisely defined mineral. A strong magnet may attract it weakly if magnetite is present, but ordinary goethite-hematite concretions are often nonmagnetic.

Field identification & locations

Identify by its rusty color, high density, earthy surface, and yellow-brown/red streak; a fresh broken face and streak test are more diagnostic than appearance alone. Common worldwide, especially in iron-rich sedimentary terrains.