sedimentary
Chert (varietal Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray to blue-gray with white patination; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray to blue-gray with white patination
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray to blue-gray with white patination; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica-rich fluids in sedimentary environments; often replaces carbonate minerals in limestone or chalk beds. Commonly dates from the Proterozoic to the Holocene.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road surfacing, as an abrasive, and sometimes in jewelry (tumbled stones).
Geological facts
Chert is so hard it will scratch glass and steel. It was the primary material for the 'Stone Age' because its conchoidal fracture creates edges sharper than a steel scalpel.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its ability to spark when struck against steel. Commonly found as nodules in limestone outcrops or as river cobbles.
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