mineral

Limonite (Yellow Ochre)

Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)

Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to brownish-orange; Luster: Dull or earthy; Crystal Structure: Amorphous (does not form visible crystals); Specific Gravity: 2.7–4.3.

Hardness: 4-5
Color: Yellowish-brown to brownish-orange
Luster: Dull or earthy

Identified March 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to brownish-orange; Luster: Dull or earthy; Crystal Structure: Amorphous (does not form visible crystals); Specific Gravity: 2.7–4.3.

Formation & geological history

Formed by the oxidation and hydration of iron-rich minerals (like pyrite or magnetite) through weathering processes. It is a secondary mineral commonly found in the oxidation zones of ore deposits and bog iron environments.

Uses & applications

Historically used as a yellow and brown pigment (ochre) in paints and dyes. It is a minor ore of iron and sometimes collected as a geological specimen representing chemical weathering.

Geological facts

Limonite is not a true mineral but a mineraloid, consisting of a mixture of hydrated iron oxides. It was one of the first pigments used by prehistoric humans in cave paintings, such as those found at Lascaux.

Field identification & locations

Identify in the field by its distinct yellow-brown streak (produced by rubbing it on unglazed porcelain) and its earthy, non-metallic appearance. Common in weathered outcrops of iron minerals and sedimentary ironstones.

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