mineral

Limonite / Ironstone

Limonite (Hydrated Iron Oxide) - FeO(OH)·nH2O

Hardness: 4-5.5; Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified May 28, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich mineral deposits (like pyrite or magnetite) in sedimentary environments.

Uses & applications

Used historically as a source of iron ore and as a pigment (yellow ochre) in paints. Today it is mostly a collector specimen or industrial iron source.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, most commonly goethite. It is responsible for the yellow and brown colors in many soils.

Field identification & locations

Identify by its characteristic 'rust' color and yellowish-brown streak on a porcelain plate. Commonly found in bog deposits or as a staining on other rocks.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

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

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral