sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or white
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.65
Formation & geological history
Formed in sedimentary rocks by the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or through chemical precipitation. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a raw material for ceramics.
Geological facts
Because of its conchoidal fracture, chert breaks into very sharp edges, which made it the primary material for arrowheads and scrapers in the Stone Age.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy luster on fresh breaks, and smooth, curved fracture surfaces. Found worldwide in creek beds and limestone outcrops.
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