sedimentary
Chert (and/or Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with waxy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic debris (like diatom or radiolarian shells) or through chemical precipitation in marine environments. It often occurs as nodules or layers within limestone and chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges when fractured. Currently used as road surfacing material, in decorative landscaping, and occasionally for fire-starting (flint).
Geological facts
Chert was one of the most important minerals for early humans. Its ability to produce a predictable, razor-sharp edge made it the premier material for the Stone Age tool industry.
Field identification & locations
Identify in the field by its very smooth, waxy surface and its tendency to break with 'shell-like' (conchoidal) curves. It will easily scratch glass and will not react with acid. Commonly found in riverbeds and limestone outcrops.
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