mineral

Limonite (Ironstone)

FeO(OH)·nH2O (Hydrous ferric oxides)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull/Earthy

Identified June 11, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed by the oxidation and hydration of iron-rich mineral ores (like pyrite or magnetite) through weathering. Common in soil horizons and Bog Iron deposits.

Uses & applications

Primary source of yellow ochre pigment for paints; historical source of iron ore for smelting; used in water filtration systems.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxides. It was used by prehistoric humans as one of the first cave-painting pigments.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusted appearance. Often found in swampy areas or gossans above ore bodies.

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

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Schist

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Epidote

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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]

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