sedimentary
Chert (Chalcedony/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Gray, brown, or tan with waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Gray, brown, or tan with waxy luster
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Gray, brown, or tan with waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation from groundwater within sedimentary rock layers, often occurring as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and fire-starting; currently used in jewelry (as jasper or agate), as a gemstone, or in construction aggregate.
Geological facts
Chert has been used by humans for hundreds of thousands of years to make arrowheads and scrapers due to its ability to break into extremely sharp edges.
Field identification & locations
Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern. It cannot be scratched by a steel knife and often sparks when struck with steel.
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