sedimentary
Chert (often called Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown, or white
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich organic remains or chemical precipitation. Primarily found in marine sedimentary layers of various ages.
Uses & applications
Historically used for stone tools (arrowheads, knives) and striking fire; currently used as a road aggregate, in glass making, and by flintknapping hobbyists.
Geological facts
Chert breaks with a conchoidal fracture, creating sharp edges that are sharper than a steel scalpel. It was one of the most important resources for prehistoric humans.
Field identification & locations
Identify by its extremely fine grain (can't see crystals), waxy feel, and the way it breaks into curved, glass-like shards. Often found in creek beds or eroding out of limestone cliffs.
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