mineral

Limonite (Ironstone Concretion)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5; 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 12, 2026More mineral →

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Physical properties

Hardness: 4-5.5; 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 precipitation of iron-bearing minerals in sedimentary environments or as a weathering product of iron-rich ores. Often found in bogs or as concretions.

Uses & applications

Historically used as a common iron ore and as a pigment (Yellow Ochre). Occasionally collected as a geological specimen.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It has been used as a pigment since prehistoric times, including in Lascaux cave paintings.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Commonly found in sedimentary basins and weathered iron deposits.

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Nephrite Jade

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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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