sedimentary

Limonite / Ironstone

FeO(OH)·nH2O

Hardness 4.0-5.5 on Mohs scale, earthy to dull or submetallic luster, dark yellowish-brown to rust-brown color, amorphous or microcrystalline structure, brownish-yellow streak.

Identified July 22, 2026More sedimentary →

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Physical properties

Hardness 4.0-5.5 on Mohs scale, earthy to dull or submetallic luster, dark yellowish-brown to rust-brown color, amorphous or microcrystalline structure, brownish-yellow streak.

Formation & geological history

Formed as a secondary mineral product from the oxidation and weathering of iron-rich rocks and primary iron minerals like pyrite, siderite, and magnetite in surface or near-surface environments.

Uses & applications

Historically used as an important ore of iron and as a yellow-brown pigment (yellow ochre). Commonly collected as a mineral specimen.

Geological facts

Limonite is not a true single mineral, but a field term for mixtures of hydrated iron oxides, predominantly goethite with lepidocrocite and quartz. It was used as pigment in prehistoric cave paintings.

Field identification & locations

Identified by its characteristic yellowish-brown streak, rusty color, earthy texture, and association with weathered iron deposits. Found in iron ores, stream beds, and weathered sedimentary strata.