sedimentary

Banded Chert / Sandstone Pebble

Microcrystalline Quartz (SiO2) / Silicified Sandstone

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, grey, and dark charcoal bands. Luster: Dull to sub-vitreous. Texture: Smooth, rounded water-worn pebble with distinct stratification lines. Cleavage: None (conchoidal to uneven fracture). Specific gravity: ~2.6-2.65.

Hardness: 6
Color: Tan, brown, grey, and dark charcoal bands
Luster: Dull to sub-vitreous

Identified July 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in a sedimentary depositional environment through the gradual accumulation and compaction of fine silica and sand layers with varying mineral impurities (e.g., iron oxides and organic material). Sub-rounded shape caused by alluvial stream or river erosion.

Uses & applications

Primarily collected as a decorative stream pebble or landscape rock. Historically, high-silica chert variants were used for flintknapping tool creation.

Geological facts

The distinct alternating light and dark bands represent historical changes in depositional environment, water chemistry, or sediment source during the rock's formation over millions of years.

Field identification & locations

Identify in the field by its distinct parallel color banding, smooth rounded surface, and high hardness (scratches glass). Common in river beds, glacial deposits, and sedimentary terraces across Europe, including Burgundy, France (Morvan/Autun area).