sedimentary
Limonite / Ironstone
Hydrated Iron Oxide (FeO(OH)·nH2O)
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.
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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.
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