sedimentary
Ironstone Concretion (Limonite/Goethite)
Ironstone (primarily FeO(OH)·nH2O)
Hardness: 4.0-5.5 on Mohs scale; Color: Dark brown to ochre yellow/orange; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
- Hardness
- 4
- Color
- Dark brown to ochre yellow/orange
- Luster
- Dull, earthy, or sub-metallic
Identified More sedimentary →
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: Dark brown to ochre yellow/orange; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
Formation & geological history
Formed by the precipitation of iron-rich minerals in the pore spaces of sedimentary rocks or through the oxidation of iron-bearing minerals. They often form in wetlands, lake beds, or shallow marine environments as nodules over millions of years.
Uses & applications
Historically used as a low-grade iron ore. Today, it is primarily used in landscaping, as a construction aggregate, or by amateur geologists for its unique aesthetic and internal banded structures.
Geological facts
These are often mistaken for meteorites because of their high density and dark, rusty appearance. However, ironstones are much softer and lack the fusion crust found on meteorites. Many concretions contain a hollow center or a different colored core.
Field identification & locations
Identify by its high weight relative to its size (heft) and its yellow-orange streak when scratched on unglazed porcelain. Commonly found in eroded riverbeds, beaches, and areas with sedimentary clay or sandstone deposits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary