mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous or cryptocrystalline; Cleavage: None; Specific Gravity: 2.7–4.3.

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

Identified March 8, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous or cryptocrystalline; Cleavage: None; Specific Gravity: 2.7–4.3.

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of other iron-bearing minerals like pyrite, magnetite, and hematite. It is commonly found in gossans (oxidized rock atop mineral deposits) and swamp environments (bog iron).

Uses & applications

Historically used as a major source of iron ore and as a pigment (yellow ochre) in paints. In construction, it is sometimes used as a flux in cement production.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It has been used by humans as a pigment for cave paintings dating back thousands of years.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusted appearance. It is ubiquitous in sedimentary environments and iron-rich soils worldwide.