sedimentary
Banded Chert / Sandstone Pebble
Microcrystalline Quartz (SiO2) / Silicified Sandstone
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
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Physical properties
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.
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).
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