mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0 - 5.5 on Mohs scale; Color: Yellowish-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
Color: Yellowish-brown to dark brown
Luster: Dull, earthy, or submetallic

Identified January 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in weathering zones. It is a secondary mineral typically found in sedimentary environments or as a 'gossan' capping metallic ore deposits.

Uses & applications

Historically used as a low-grade iron ore. In industry, it is primarily used as a pigment (yellow ochre) for paints and dyes. It is also used in the production of cement and as a soil conditioner.

Geological facts

Limonite is not a true mineral but a mineraloid composed of a mixture of hydrated iron oxides. It was a major source of iron for early civilizations and is the substance that gives many soils their yellow or brown color.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusted appearance. It is commonly found in boggy areas (bog iron) and weathering outcrops of iron-bearing rocks. Collect specimens that show interesting botryoidal (grape-like) or 'rusty' textures.