sedimentary
Siltstone with Concretion
Siltstone (composed of hydraulic silicates and quartz particles)
Hardness: 3-6 Mohs. Color: Grey with a yellowish-brown circular inclusion. Luster: Dull/Earthy. Structure: Fine-grained clastic texture. Cleavage: None, breaks with sub-conchoidal fracture.
- Hardness
- 3-6 Mohs
- Color
- Grey with a yellowish-brown circular inclusion
- Luster
- Dull/Earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-6 Mohs. Color: Grey with a yellowish-brown circular inclusion. Luster: Dull/Earthy. Structure: Fine-grained clastic texture. Cleavage: None, breaks with sub-conchoidal fracture.
Formation & geological history
Formed by the deposition and lithification of silt-sized particles in aqueous environments like river deltas or lake beds. The central 'eye' or concretion forms by mineral precipitation around a nucleus during diagenesis.
Uses & applications
Primarily used for landscape gravel or construction fill. Smooth river-worn specimens are often kept as worry stones or curiosities.
Geological facts
The circular feature is a concretion, which is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles. These can often mimic fossils or eyes.
Field identification & locations
Look for fine grains that are smaller than sand but gritty to the touch (unlike clay). The circular feature is harder than the surrounding matrix and may show concentric rings. Found in riverbeds and eroded cliffsides.
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