sedimentary

Limonite Geode (Ironstone Concretion)

Limonite [FeO(OH)·nH2O] with possible Quartz or Calcite interior

Hardness: 4-5.5 (Limonite shell); Color: Yellowish-brown to dark brown exterior, white/translucent interior. Luster: Dull or earthy shell, vitreous core. Crystal structure: Amorphous to microcrystalline. Cleavage: None.

Hardness: 4-5
Luster: Dull or earthy shell, vitreous core

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the precipitation of iron-rich minerals (limonite/goethite) around a nucleus in sedimentary environments, often in soils or shallow bogs during the Holocene to Pleistocene epochs.

Uses & applications

Primary source of iron ore historically; used in mineral pigment production (yellow ochre) and as a collector's specimen for demonstrating sedimentary processes.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was once the most important source of iron for early human civilizations and remains a major pigment source.

Field identification & locations

Identify by its characteristic yellowish-brown 'ochre' color and relatively high density for its size. Often found in stream beds or weathered sedimentary outcrops. Look for 'rust' staining on hands after handling.

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