sedimentary

Limonite or Ironstone Nodule

FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5; Color: Dark brown to earthy yellow; Luster: Dull, earthy; Crystal Structure: Amorphous or cryptocrystalline; Specific Gravity: 2.7-4.3

Hardness: 4
Color: Dark brown to earthy yellow
Luster: Dull, earthy

Identified July 2, 2026More sedimentary →

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Physical properties

Hardness: 4.0-5.5; Color: Dark brown to earthy yellow; Luster: Dull, earthy; Crystal Structure: Amorphous or cryptocrystalline; Specific Gravity: 2.7-4.3

Formation & geological history

Formed by the oxidation of iron-rich mineral deposits or through the precipitation of iron from groundwater in sedimentary environments like marshes or streambeds.

Uses & applications

Historically used as an iron ore; currently used as a natural earth pigment (ochre) and as low-value geological specimens for teaching.

Geological facts

Limonite is not a true mineral but a mineraloid. It was one of the first pigments used by early humans in cave paintings, such as those at Lascaux.

Field identification & locations

Identified by its yellow-brown streak on a porcelain plate and its earthy, non-metallic appearance. Common in boggy areas and oxidized zones of ore deposits.