sedimentary

Limonite (Ironstone)

FeO(OH)qn H2O

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown or rusty orange; Luster: Dull or earthy; Structure: Amorphous or microcrystalline; Cleavage: None; Streak: Yellowish-brown.

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

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown or rusty orange; Luster: Dull or earthy; Structure: Amorphous or microcrystalline; Cleavage: None; Streak: Yellowish-brown.

Formation & geological history

Formed through the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in acidic or weathering environments. It is a secondary mineral commonly found in oxidised zones of ore deposits.

Uses & applications

Historically used as a low-grade iron ore and as a source of yellow ochre pigment for paints. Today, it is primarily of interest to collectors or as a soil constituent.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, mostly Goethite. It is often found in 'gossans' (iron hats) that cap sulfide ore deposits.

Field identification & locations

Identify in the field by its distinct yellow-brown streak and earthy appearance. Found worldwide in areas of heavy weathering or wet environments like bogs (bog iron).