sedimentary
Chert (often called Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray to blue-gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray to blue-gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray to blue-gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation. Primary occurrence is within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used for decorative stone, road surfacing, and as a preferred material for arrowheads and knapping.
Geological facts
Chert is so hard it can scratch steel. When broken, it creates exceptionally sharp edges, which led to its widespread use in the Stone Age for tools and weapons.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass. Found globally, especially in areas with ancient limestone deposits.
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