mineral

Weathered iron-rich concretion (probable limonite/goethite)

Limonite–goethite aggregate, approximately FeO(OH)·nH₂O

AI-generated identification · may be incorrect

Hardness roughly 4–5.5 Mohs; dull earthy luster, gray-brown to rusty orange color, irregular botryoidal/concretionary surface, and no visible crystal cleavage. The dense, rounded form and iron staining are characteristic of hydrated iron oxides.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed when iron-bearing groundwater precipitated oxides and hydroxides around a nucleus in soil or sediment, followed by weathering and rounding. Its exact geological age cannot be determined from the photograph.

Uses & applications

Common specimens have little industrial or jewelry value, though iron-oxide minerals are minor iron ores and are used as natural pigments. Attractive botryoidal pieces may interest collectors.

Geological facts

“Limonite” is a field term for a mixture of hydrated iron oxides rather than one precisely defined mineral. Goethite commonly produces yellow-brown to dark rusty surfaces.

Field identification & locations

Common in weathered soils, sedimentary rocks, bogs, and mine-dump areas worldwide. A rusty streak on unglazed porcelain, relatively high density, and lack of fizz with dilute acid help distinguish it from many ordinary stones; a magnet test may be weak or negative.