sedimentary

Limonite

Hydrous ferric oxides (FeO(OH)·nH2O)

Hardness: 4 to 5.5 (Mohs scale), Color: Yellowish-brown to brownish-black, Luster: Dull to earthy, Crystal Structure: Amorphous (pseudomorphous), Cleavage: None, Specific Gravity: 2.7 to 4.3

Hardness: 4 to 5

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 4 to 5.5 (Mohs scale), Color: Yellowish-brown to brownish-black, Luster: Dull to earthy, Crystal Structure: Amorphous (pseudomorphous), Cleavage: None, Specific Gravity: 2.7 to 4.3

Formation & geological history

Formed by the oxidation and hydration of iron-rich mineral deposits (like pyrite, magnetite, or hematite) in the presence of water and oxygen. It is often found in the gossan (iron cap) of ore deposits and in bog iron environments.

Uses & applications

Historically used as an ore of iron and as a natural pigment (yellow ochre). Today, it is primarily of interest to mineral collectors and as a source of iron oxide pigments.

Geological facts

Limonite is not a true mineral but a mixture of similar hydrated iron oxide minerals, mostly goethite. It was the primary source of iron for many early civilizations and was used by ancient humans as a paint pigment, known as 'ochre'.

Field identification & locations

Identify in the field by its distinctive yellowish-brown streak (produced by rubbing it on an unglazed ceramic plate) and its earthy, rusty appearance. It is extremely common worldwide in weathering zones of rocks.