sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale), Color: tan, grey, brown, white
- Color
- tan, grey, brown, white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, as jewelry (if colorful), and as an abrasive.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges for hunting and scraping. It is chemically very resistant to weathering.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy surface with curved fracture edges. Commonly found in riverbeds and limestone outcrops.
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