sedimentary

Siltstone with Concretion

Siltstone (composed of hydraulic silicates and quartz particles)

AI-generated identification · may be incorrect

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 May 28, 2026More sedimentary →

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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.