sedimentary
Banded Chert
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Grey, tan, and light green bands; Luster: Dull to waxy; Crystal structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Grey, tan, and light green bands
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Grey, tan, and light green bands; Luster: Dull to waxy; Crystal structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in marine environments. Banding represents seasonal or environmental shifts in deposition.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; currently used for decorative stones, aquarium gravel, and occasionally as a low-cost gemstone or for lapidary work.
Geological facts
Chert is a chemical sedimentary rock. The banding, often called 'ribbon chert,' is frequently found in tectonic zones where oceanic crust was scraped off onto continents.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy feel, and the distinctive conchoidal (shell-like) fracture pattern. Commonly found in riverbeds, coastal cliffs, and limestone formations.
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