sedimentary
Fossiliferous Chert
Silicon Dioxide (SiO2) with fossil inclusions
Hardness: 7; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque to translucent.
- Hardness
- 7
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque to translucent.
Formation & geological history
Formed through the chemical precipitation of silica or the accumulation of silica-rich organic debris (diatoms/radiolarians) in marine environments. The curved shape and internal patterns suggest a fossil fragment, likely a shell or crinoid piece, replaced by silica.
Uses & applications
Collecting, historical tool-making (flint knapping), and small decorative items.
Geological facts
This specimen appears to be a 'steinkern' or an internal cast of a marine organism. Chert is often used as a catch-all term for microcrystalline quartz that forms in sedimentary nodules.
Field identification & locations
Look for the waxy texture and inability to be scratched by a steel blade. Often found in limestone or chalk beds and along riverbanks/beaches where the harder silica survives erosion better than the host rock.
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