sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: multi-toned tan, brown, and grey with a white/pinkish center; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture)
- Hardness
- 7 Mohs scale
- Color
- multi-toned tan, brown, and grey with a white/pinkish center
- Luster
- waxy to vitreous
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Physical properties
Hardness: 7 Mohs scale; Color: multi-toned tan, brown, and grey with a white/pinkish center; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture)
Formation & geological history
Forms through the accumulation of silica-rich microfossils or chemical precipitation in marine or freshwater environments. This specimen appears water-worn and polished by river or stream action.
Uses & applications
Historically used for making sharp tools and weapons; currently used for decorative garden stones, tumbling, and as a durable construction aggregate.
Geological facts
Chert is one of the most durable sedimentary rocks. When struck against steel, it can create sparks, making it useful for fire-starting in survival situations.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and smooth, waxy feel. Commonly found in riverbeds, glacial deposits, and as nodules within limestone formations.
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