sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Grey, brown, and tan with slight variegation, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Grey, brown, and tan with slight variegation, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen appears water-worn or tumbled, likely from a fluvial (river) or coastal deposit.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Modern uses include decorative gravel, lapidary tumbling, and high-quality industrial grinding media.
Geological facts
Chert is so durable that it often survives as pebbles long after the surrounding rock has weathered away. Ancient people worldwide prized it for making arrowheads and spear points.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy luster when smooth, and distinctive curved (conchoidal) breaks. Often found in riverbeds or coastal beaches as smooth pebbles.
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