mineral

Limonite (Iron Ore)

Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (lacks definite crystal structure); Streak: Yellow-brown; Specific Gravity: 2.7 - 4.3

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

Identified June 21, 2026More mineral →

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Physical properties

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (lacks definite crystal structure); Streak: Yellow-brown; Specific Gravity: 2.7 - 4.3

Formation & geological history

Formed usually from the oxidation and hydration of iron-rich sulfide minerals (like pyrite) or as a chemical precipitate in shallow marine or bog environments (bog iron).

Uses & applications

A minor ore of iron; used as a natural earth pigment (yellow ochre) in paints, dyes, and cosmetics. Primarily collected as a secondary mineral or historical iron source.

Geological facts

Limonite is not a true mineral but a mixture of related hydrated iron oxide minerals. It was one of the first pigments used by early humans in cave paintings, such as at Lascaux.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its dull, ochre-like appearance. Commonly found in gossans (weathered tops of ore deposits) and sedimentary layers.

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