sedimentary
Chert (Flint)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, gray, and cream with waxy luster; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, gray, and cream with waxy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, gray, and cream with waxy luster; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Ages vary from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for decorative stone, landscaping, and flint-knapping enthusiasts.
Geological facts
Chert exhibits conchoidal fracture, meaning it breaks like glass to create razor-sharp edges. It was one of the most important minerals for early humans.
Field identification & locations
Identify by its waxy appearance, extreme hardness (scratches glass), and shell-like fracture pattern. Often found as nodules within limestone or chalk beds.
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