sedimentary
Chert (often called Flint or Jasper)
Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan (as seen in image); Luster: waxy to dull; Structure: microcrystalline quartz; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- typically grey, brown, or tan (as seen in image)
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan (as seen in image); Luster: waxy to dull; Structure: microcrystalline quartz; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.
Uses & applications
Historically used for stone tools and arrowheads; modernly used as a decorative landscaping stone, in road construction, and as a component in glass manufacturing.
Geological facts
Because it breaks with a conchoidal fracture, it creates sharp edges used by prehistoric humans for hunting and survival. The variation known as 'flint' was essential for starting fires and for flintlock firearms.
Field identification & locations
Identify in the field by its characteristic 'shell-like' curved fractures (conchoidal) and its ability to scratch glass. Commonly found in nodules within limestone outcrops or as river-worn pebbles.
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