Mineral

Limonite (Iron Ore)

Limonite (mixture of hydrated iron(III) oxide-hydroxides)

Hardness: 4-5.5 (Mohs scale); Color: Yellow-brown to dark brown; Luster: Dull, earthy, or submetallic; Crystal Structure: Amorphous (lacks definite crystal shape); Cleavage: None; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Yellow-brown to dark brown
Luster: Dull, earthy, or submetallic

Identified June 17, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary material through the oxidation or weathering of primary iron-bearing minerals like pyrite or magnetite. It is common in soil and boggy environments as sedimentary deposits.

Uses & applications

A major ore of iron historically used for pigments (yellow ochre) and occasionally in iron production. Significant in industrial history for making wrought iron.

Geological facts

Limonite was a primary source of iron for over 2,500 years and is the main component of 'bog iron'. It is also one of the substances that gives Mars its reddish-brown color.

Field identification & locations

Identify by its brownish-yellow streak on a porcelain plate and its earthy, often concretionary or botryoidal appearance. Found worldwide in oxidised zones of metallic deposits.

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