sedimentary
Chert (River Pebble with Liesegang Rings)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.
- Hardness
- 6
- Color
- Tan, brown, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.
Formation & geological history
Formed via the accumulation of siliceous remains of diatoms or radiolarians, or through chemical precipitation in marine or groundwater environments. Common in Phanerozoic sedimentary sequences.
Uses & applications
Historically used for stone tools and strike-a-lights; currently used in decorative landscaping, as river rock, and as common collector specimens.
Geological facts
The brown patterns are likely Liesegang rings, which are secondary rhythmic chemical precipitates formed during fluid flow through porous rock. Chert is the same material as flint, but usually lighter in color.
Field identification & locations
Identify by its hardness (scratches glass), waxy texture when wet, and smooth, rounded shape if found in rivers or beaches. Very common in outwash plains and riverbeds.
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