mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs); Color: yellow-brown to dark brown; Luster: dull to earthy; Crystal Structure: Amorphous/microcrystalline; Cleavage: none; Specific Gravity: 2.7–4.3

Hardness: 4-5
Color: yellow-brown to dark brown
Luster: dull to earthy

Identified March 14, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs); Color: yellow-brown to dark brown; Luster: dull to earthy; Crystal Structure: Amorphous/microcrystalline; Cleavage: none; Specific Gravity: 2.7–4.3

Formation & geological history

Formed by the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) through weathering. Common in boggy environments and gossans (iron hats).

Uses & applications

Major source of iron ore; historically used as a primary yellow-ochre pigment in paints and dyes; used in drilling mud in the oil industry.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxides. It has been used by humans as a pigment since prehistoric times, notably in cave paintings.

Field identification & locations

Identify by its yellowish-brown streak on a ceramic plate. Found globally in iron-rich sedimentary deposits. Collectors look for 'pseudomorph' specimens where it replaces other crystals.