mineral

Limonite (Ironstone)

FeO(OH)nH₂O (composed mainly of goethite)

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous; Streak: Yellowish-brown

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

Identified June 10, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous; Streak: Yellowish-brown

Formation & geological history

Formed by the oxidation and hydration of iron-rich sulfide minerals (like pyrite) or as a secondary pigment in sedimentary rocks. Found in oxic zones of ore deposits and swamps.

Uses & applications

Historical source of iron ore (bog iron); used as a pigment (yellow ochre) in paints and ceramics.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxides. It has been used as a pigment since prehistoric times in cave paintings.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its rusty appearance. Often found as a coating on or filling in other rocks.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic