mineral

Limonite/Ironstone

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (it is a mineraloid mixture); Specific Gravity: 2.7-4.3.

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull to earthy

Identified May 31, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (it is a mineraloid mixture); Specific Gravity: 2.7-4.3.

Formation & geological history

Formed by the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in weathering zones or as a chemical precipitate in damp sedimentary environments.

Uses & applications

Historically used as a major source of iron ore; currently used as an ochre pigment for paints and in cement production.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It is often responsible for the 'rust' color seen in desert landscapes and on the surface of Mars.

Field identification & locations

Identify in the field by its yellow-brown streak (even on dark specimens) and lack of magnetism compared to magnetite. Commonly found in boggy areas and oxidized zones of ore deposits.