sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on the Mohs scale
- Color
- Gray, tan, or brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on the Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation in sedimentary environments. Common in marine limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in jewelry (tumbled stones), high-end construction gravel, and as a geological collecting specimen.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's scalpel. It is the official state rock of Ohio (as Flint Ridge flint).
Field identification & locations
Identify in the field by its waxy appearance and 'shell-like' curved breaks (conchoidal fracture). It will easily scratch glass and cannot be scratched by a steel knife.
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