mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0 - 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull, earthy, or submetallic; Crystal Structure: Amorphous (often pseudomorphs after other minerals); Cleavage: None; Specific Gravity: 2.7 - 4.3.

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

Identified March 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral through the weathering of iron-rich minerals such as pyrite, magnetite, and hematite in oxidation zones. It can form in various geological ages and is common in sedimentary bog deposits and gossans.

Uses & applications

Historically used as a major ore of iron; currently used as a pigment (yellow ochre) in paints, dyes, and as a soil conditioner in agriculture.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron(III) oxide-hydroxides. It was the primary source of 'Yellow Ochre' used in prehistoric cave paintings, such as those in Lascaux, France.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak and earthy appearance. It often stains surrounding rocks or water orange. Common in swampy areas or near mining tailings. Collectors look for 'pseudomorphs' where limonite has replaced cubic pyrite gems.