mineral

Limonite (Iron Ore)

Limonite (Hydrous Ferric Oxides, FeO(OH)nH2O)

Hardness: 4.0-5.5; Color: Yellow-brown to ochre; Luster: Earthy, dull; Crystal structure: Amorphous to cryptocrystalline; Cleavage: None; Specific gravity: 2.7-4.3

Hardness: 4
Color: Yellow-brown to ochre
Luster: Earthy, dull

Identified May 24, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5; Color: Yellow-brown to ochre; Luster: Earthy, dull; Crystal structure: Amorphous to cryptocrystalline; 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. It is commonly found in gossans (iron hats) above ore deposits.

Uses & applications

Used primarily as a low-grade iron ore and as a natural earth pigment (Yellow Ochre) for paints and dyes. Historical importance as a source of iron for bloomery furnaces.

Geological facts

Limonite is not a true mineral in the strict sense but a mixture of related hydrated iron oxide minerals, predominantly goethite. It gives Mars its characteristic reddish-orange surface tint.

Field identification & locations

Identify by its distinctive yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Often found in boggy areas or weathered rock outcrops.

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