mineral

Limonite (Ironstone)

Limonite (FeOO·nH2O)

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown or blackish, Luster: Dull to earthy, Crystal Structure: Amorphous (no visible crystals), Cleavage: None, Specific Gravity: 2.7–4.3

Hardness: 4-5

Identified July 1, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown or blackish, Luster: Dull to earthy, Crystal Structure: Amorphous (no visible crystals), Cleavage: None, Specific Gravity: 2.7–4.3

Formation & geological history

Formed as a secondary mineral through the weathering of various iron oxides, sulphides, and carbonates. Often found as a bog ore in marshes or as a weathered 'gossan' capping mineral deposits.

Uses & applications

Primarily used as an ore of iron and as a natural earth pigment known as yellow ochre for paints and dyes. Historically used in primitive metallurgy.

Geological facts

Limonite is not a singular mineral species but a mixture of hydrated iron oxide minerals, primarily goethite. It has been used by humans as an artistic pigment for over 30,000 years, appearing in prehistoric cave paintings.

Field identification & locations

Identify by its distinctive yellow-brown streak (even if the rock looks dark). It is often heavy for its size and lacks a crystalline habit. Commonly found in river beds, soil, and areas with high iron content in the water table.