sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/greasy luster; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or tan with waxy/greasy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/greasy luster; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or sponges) on the ocean floor or through chemical precipitation in limestone or dolomite beds. Often found as nodules or layers.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road aggregate, decorative landscaping, and as a component in glass and ceramics.
Geological facts
Chert is a 'standard' for prehistoric toolmaking because of its predictable conchoidal fracture which creates razor-sharp edges. It can spark when struck against steel, leading to its name 'flint' in common parlance.
Field identification & locations
Identify by its hardness (will scratch glass), waxy feel, and sharp, curved (conchoidal) edges when broken. It is extremely common in areas with limestone bedrock across North America and Europe.
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