mineral

Limonite (Yellow Ochre)

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

Hardness: 4.0-5.5 (Mohs scale); Color: Yellow to brownish-yellow; Luster: Dull or earthy; Crystal Structure: Amorphous (does not form distinct crystals); Cleavage: None; Specific Gravity: 2.7 to 4.3.

Hardness: 4
Color: Yellow to brownish-yellow
Luster: Dull or earthy

Identified March 15, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Yellow to brownish-yellow; Luster: Dull or earthy; Crystal Structure: Amorphous (does not form distinct crystals); Cleavage: None; Specific Gravity: 2.7 to 4.3.

Formation & geological history

Limonite is formed as a secondary mineral through the weathering and oxidation of other iron-bearing minerals like pyrite or magnetite. It is found in oxidation zones of iron ore deposits and in biological environments like bogs and lakewaters.

Uses & applications

Primarily used as an iron ore and historically as a pigment for yellow ochre paint. In modern industry, it is used in the manufacturing of cement and as a source for iron in smelting.

Geological facts

Limonite is not a true mineral but a mineraloid. It was famously used as a prehistoric cave painting pigment and was once the source of 'bog iron' which fueled the Iron Age in Northern Europe.

Field identification & locations

Identify in the field by its distinct yellow-brown streak (test on unglazed porcelain) and earthy appearance. It is commonly found in tropical soils (laterites) and near metallic mineral veins.

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