sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with possible banding; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey with possible banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with possible banding; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (knapping); modernly used for road aggregate, landscaping, and occasionally lapidary work or semi-precious jewelry.
Geological facts
Chert is so hard it can strike sparks against steel, making it a primary material for 'flint and steel' fire starting and early firearms (flintlocks).
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel blade. Commonly found in limestone or chalk beds and along riverbanks/beaches.
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