sedimentary

Limonite / Ironstone Nodule

Hydrated Iron Oxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0 - 5.5 on Mohs scale. Color: Yellowish-brown, dark brown, or reddish-brown. Luster: Earthy, dull, or submetallic. Streak: Yellowish-brown. Specific gravity: 2.7 - 4.3.

Hardness: 4
Color: Yellowish-brown, dark brown, or reddish-brown
Luster: Earthy, dull, or submetallic

Identified July 24, 2026More sedimentary →

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Physical properties

Hardness: 4.0 - 5.5 on Mohs scale. Color: Yellowish-brown, dark brown, or reddish-brown. Luster: Earthy, dull, or submetallic. Streak: Yellowish-brown. Specific gravity: 2.7 - 4.3.

Formation & geological history

Formed through the weathering and oxidation of iron-rich minerals (such as pyrite, marcasite, or siderite) in sedimentary environments, riverbeds, and weathered soil zones.

Uses & applications

Historically used as a secondary iron ore and natural earth pigment (yellow ochre). Today, it is primarily collected by rockhounds as a mineral specimen.

Geological facts

Limonite is not a true single mineral, but rather a field term for a mixture of related hydrated iron oxides, principally goethite. It often forms pseudo-morphs, taking over the crystal shape of other minerals.

Field identification & locations

Look for a distinctive earthy brown to yellowish texture with a characteristic yellow-brown streak when scratched against unglazed porcelain. Extremely common in stream beds, soil zones, and sedimentary formations globally.