mineral

Weathered ironstone concretion (probable limonite/goethite nodule)

Limonite-goethite-rich iron-oxide concretion; chiefly FeO(OH)·nH₂O

AI-generated identification · may be incorrect

Hardness about 4–5.5 Mohs; tan to rusty brown, earthy to dull/vitreous luster, massive with no obvious crystal faces or cleavage. Likely dense relative to ordinary soil and may leave a yellow-brown streak; exact identification requires streak, magnetism, and specific-gravity tests.

Identified August 27, 2026More mineral →

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Physical properties

Formation & geological history

Forms when dissolved iron precipitates and cements sediment or soil, commonly through weathering and groundwater movement; it may be geologically young or derived from much older bedrock. The rounded, irregular shape suggests a transported or soil-formed concretion rather than a crystalline mineral specimen.

Uses & applications

Mostly collected as a geological curiosity or used as an iron-oxide pigment; generally unsuitable for jewelry or construction unless part of an iron-rich ore deposit.

Geological facts

Limonite is a variable mixture rather than a single definite mineral, while goethite is a specific iron oxyhydroxide. A reddish-brown streak and occasional weak magnetism after heating support an iron-oxide identification.

Field identification & locations

Common in soils, laterites, weathered iron-rich rocks, and sedimentary deposits worldwide; cut surfaces may show concentric layering. It could also be a non-geological clay or soil lump, so a fresh streak test and hardness test are recommended.