sedimentary

Limonite / Ironstone Concretion

Hydrated Iron Oxide (FeO(OH)·nH2O)

Hardness 4-5.5 on Mohs scale; yellowish-brown to dark brown with an earthy to submetallic luster; typically amorphous or microcrystalline.

Identified October 25, 2026More sedimentary →

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Physical properties

Hardness 4-5.5 on Mohs scale; yellowish-brown to dark brown with an earthy to submetallic luster; typically amorphous or microcrystalline.

Formed as secondary weathering products of iron-bearing minerals or by precipitation in bog and sedimentary environments.

Historically mined as a minor iron ore and ground into yellow ochre pigment for paints and dyes.

Limonite is not a true single mineral but a field term for a mixture of hydrated iron oxides, predominantly goethite.

Identified in the field by its distinct yellow-brown streak, irregular nodular habit, and association with weathered soils or sedimentary beds.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)