mineral

Limonite (Iron Ore)

Limonite (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 (no visible crystals); Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified April 10, 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 (no visible crystals); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary material through the oxidation or weathering of other iron-bearing minerals (like pyrite or magnetite). Often found in bog deposits or weathered outcrops.

Uses & applications

Historically used as an iron ore; currently used as a pigment (ochre) for paints and dyes. Large deposits are mined for steel production.

Geological facts

Limonite is not a true mineral but a mixture of similar hydrated iron oxides (mostly Goethite). It was used by prehistoric humans as a cave painting pigment.

Field identification & locations

Identify by its 'rust' color and yellowish-brown streak on a porcelain plate. Common in boggy areas or as 'iron hats' (gossans) on top of ore deposits. It is heavy for its size compared to organic matter.

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