mineral

Limonite (Iron Ore)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to blackish; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7–4.3

Hardness: 4-5
Color: Yellowish-brown to blackish
Luster: Dull to earthy

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to blackish; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7–4.3

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich mineral deposits (like pyrite or magnetite) in sedimentary environments or as bog iron in swamps.

Uses & applications

Historically used as a major source of iron ore; currently used as a pigment (yellow ochre) in paints, ceramics, and concrete dyes.

Geological facts

Limonite is not a true mineral but a 'mineraloid' as it lacks a definite crystal structure. It is the primary component of the pigment 'Ochre' which has been used by humans since prehistoric times for cave paintings.

Field identification & locations

Identify by its brownish-yellow streak on a porcelain plate and its rusty, earthy appearance. Commonly found in oxidized zones of ore deposits and sedimentary basins worldwide.

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