mineral

Limonite (Iron Ore)

FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often found in botryoidal or earthy masses); Specific Gravity: 2.7-4.3

Hardness: 4
Color: Yellowish-brown to dark brown
Luster: Dull to earthy

Identified July 11, 2026More mineral →

Explore Limonite (Iron Ore) in the encyclopedia →

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: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often found in botryoidal or earthy masses); Specific Gravity: 2.7-4.3

Formation & geological history

Formed by the oxidation and hydration of iron-rich mineral sulfides (like pyrite) through weathering and secondary precipitation in sedimentary or metamorphic environments.

Uses & applications

Historically used as a major source of iron ore; remains important as an earth pigment (ochre) for paints and dyes.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was the source of yellow ochre used by prehistoric humans in cave paintings.

Field identification & locations

Identified by its signature yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Commonly found in gossans (weathered tops of ore deposits) and marshy areas as 'bog iron'.