sedimentary
Chert (Jasper) Pebble
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: reddish-brown, tan, and grey; Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 7 Mohs
- Color
- reddish-brown, tan, and grey
- Luster
- dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: reddish-brown, tan, and grey; Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Forms via the precipitation of silica in sedimentary environments, often associated with marine deposits or terrestrial groundwater movement through limestone or volcanic ash. This specimen appears water-worn.
Uses & applications
Mainly used as decorative gravel, in landscaping, or as tumbled stones for hobbyist collections. Historically used for stone tools due to its sharp fracture edges.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and along beaches, which is why it is often found as smooth, rounded pebbles far from its source rock.
Field identification & locations
Identify by its high hardness (scratches glass), smooth texture, and smooth curved (conchoidal) fractures if broken. Common on riverbeds and coastal beaches worldwide.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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