sedimentary
Ironstone / Limonite Concretion
Hydrated Iron Oxide Rock (FeO(OH)·nH2O with SiO2)
Hardness: 4.0-5.5 on Mohs scale. Color: Yellowish-brown, reddish-orange, and dark brown to black crust. Luster: Earthy to dull. Cleavage: None. Density: Variable, moderately heavy due to iron content.
- Hardness
- 4
- Luster
- Earthy to dull
Identified More sedimentary →
Explore Ironstone / Limonite Concretion in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 4.0-5.5 on Mohs scale. Color: Yellowish-brown, reddish-orange, and dark brown to black crust. Luster: Earthy to dull. Cleavage: None. Density: Variable, moderately heavy due to iron content.
Formation & geological history
Formed through the precipitation of iron-rich fluids in sedimentary basins, often creating concentric layers or ironstone crusts through weathering and oxidation processes.
Uses & applications
Historically mined as low-grade iron ore. Popular among mineral collectors, for decorative landscaping, and occasionally as a source of natural ochre pigment.
Geological facts
Ironstone concretions often feature a dark, hard iron-rich rind surrounding a lighter earthy core, sometimes forming hollow structures called 'rattlestones'.
Field identification & locations
Identified by its distinctive rusty reddish-orange weathering crust, density, and yellowish-brown streak test. Commonly found in sedimentary sandstone, shale, and clay beds globally.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale
Argillaceous sedimentary rock
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary