sedimentary
Banded Chert
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, and grey banding; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Brown, tan, and grey banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Brown, tan, and grey banding; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, followed by compaction and diagenesis. Usually found in Paleozoic or Mesozoic strata.
Uses & applications
Historically used for stone tools and weapons (flint-knapping); currently used for decorative landscaping, gravel, and as a collector's specimen.
Geological facts
Chert is so durable that it often remains intact as river pebbles long after the surrounding limestone or shale has weathered away. The bands represent changes in the depositional environment.
Field identification & locations
Identify by its hardness (it will scratch glass) and its smooth, waxy feel when wet. Found globally in sedimentary basins, riverbeds, and coastal areas.
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