sedimentary
Banded Chert / Cryptocrystalline Quartz
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs). Color: Multi-colored bands (teal, white, reddish-brown). Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Multi-colored bands (teal, white, reddish-brown)
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Multi-colored bands (teal, white, reddish-brown). Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in marine or volcanic environments. The colors reflect mineral impurities like iron (red) and chlorite or copper silicates (green/teal).
Uses & applications
Collecting, lapidary use (cabbing and polishing), and historically used for stone tools due to its sharp conchoidal edges.
Geological facts
This specimen displays distinct primary layering known as banding, which often represents changes in sediment deposition or fluid chemistry over time.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel), waxy feel, and sharp, shell-like fracture edges. Found worldwide in sedimentary nodules or bedded layers.
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