sedimentary

Limonite / Ironstone

Hydrated Iron Oxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness 4-5.5 on Mohs scale; earthy to dull luster; yellowish-brown to orange-brown color; amorphous or microcrystalline structure; yellow-brown streak; specific gravity 2.7-4.3.

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness 4-5.5 on Mohs scale; earthy to dull luster; yellowish-brown to orange-brown color; amorphous or microcrystalline structure; yellow-brown streak; specific gravity 2.7-4.3.

Formation & geological history

Formed by the weathering, oxidation, and hydration of iron-rich minerals such as pyrite, marcasite, or magnetite in sedimentary or near-surface weathering environments (gossans).

Uses & applications

Historically used as an iron ore and as a natural earth pigment (yellow ochre). Commonly used as a mineral specimen for educational collections.

Geological facts

Limonite is not a true mineral in the strict chemical sense, but rather a field term for a mixture of related hydrated iron oxide minerals including goethite, lepidocrocite, and jarosite.

Field identification & locations

Identified by its distinctive yellowish-brown rust color, dull earthy surface texture, and yellow-brown streak when scratched against porcelain. Found worldwide in sedimentary iron formations and weathered zones.