sedimentary
Chert (Chert / Flint nodule)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, tan, or white with waxy appearance; Luster: dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal (shell-like) fracture; Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically grey, tan, or white with waxy appearance
- Luster
- dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, tan, or white with waxy appearance; Luster: dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal (shell-like) fracture; Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. These specimens typically form as nodules within limestone or chalk beds and can range from many millions to hundreds of millions of years in age.
Uses & applications
Historically used for stone tools and arrowheads; currently used as a road aggregate, in glass manufacturing (when high purity), and sometimes as an abrasive or in decorative landscaping.
Geological facts
Chert was one of the most important minerals to prehistoric humans because it fractures into extremely sharp edges perfect for knives and scrapers. When it strikes steel, it can produce sparks, leading to its common use in 'flint and steel' fire starting.
Field identification & locations
Identify by its extreme hardness (it will scratch glass and steel) and its shell-like, curved fracture patterns. Commonly found in areas with limestone bedrock or in river gravels where harder rocks have resisted erosion.
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