sedimentary
Banded Chert
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey with distinct parallel banding. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Tan, brown, and grey with distinct parallel banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and grey with distinct parallel banding. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids in marine environments. This specimen appears water-worn, likely from a riverbed or glacial till.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include aquarium gravel, landscaping, and lapidary work (polishing for jewelry or display).
Geological facts
Chert is so durable that it often survives millions of years of erosion that destroys the surrounding limestone. 'Flint' is a dark variety of chert often found in chalk deposits.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), waxy feel, and the way it breaks into smooth, curved surfaces. Common in river beds and sedimentary basins worldwide.
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