mineral

Limonite (Iron Ore)

Limonite (FeO(OH)nH2O)

Hardness: 4.0–5.5; Color: Yellow-brown to dark brown/black; Luster: Dull to earthy; Crystal Structure: Amorphous (often pseudomorphic); Cleavage: None; Specific Gravity: 2.7–4.3.

Hardness: 4
Color: Yellow-brown to dark brown/black
Luster: Dull to earthy

Identified April 7, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 4.0–5.5; Color: Yellow-brown to dark brown/black; Luster: Dull to earthy; Crystal Structure: Amorphous (often pseudomorphic); Cleavage: None; Specific Gravity: 2.7–4.3.

Formation & geological history

Forms primarily 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. Can be any age from Precambrian to modern-day surface deposits.

Uses & applications

Historically used as a major source of iron ore; currently used as a pigment (ocher) in paints, for purification of coal gas, and as a low-value collector specimen.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide hydroxides. It has been used as a pigment by humans since prehistoric times, famously seen in Lascaux cave paintings.

Field identification & locations

Identify in the field by its characteristic yellow-brown streak, earthy appearance, and lack of magnetism compared to magnetite. Found globally in oxidized zones of ore deposits and sedimentary basins.