sedimentary
Limonite / Ironstone Concretions
Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)
AI-generated identification · may be incorrectHardness 4–5.5; earthy to dull luster; yellowish-brown to dark rusty brown color; amorphous/microcrystalline with a distinctive yellowish-brown streak.
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Physical properties
Hardness 4–5.5; earthy to dull luster; yellowish-brown to dark rusty brown color; amorphous/microcrystalline with a distinctive yellowish-brown streak.
Formation & geological history
Formed as secondary weathering products of iron-bearing minerals or precipitated from iron-rich groundwater in sedimentary soils and sandstone.
Uses & applications
Historically mined as a low-grade iron ore and used as raw material for natural earth pigments (yellow ochre).
Geological facts
Limonite is not a true mineral species but a field term for a mixture of hydrated iron oxides, predominantly goethite.
Field identification & locations
Identified by its ochre-brown color, rough earthy texture, and yellowish streak on unglazed porcelain; extremely common worldwide in weathered soils and stream beds.
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