sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Charcoal grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Charcoal grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of silica-rich fluids in sedimentary environments, often within limestone or chalk beds. It can also form from the accumulation of silica-based micro-fossils like radiolarians.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as high-quality flint for sparking in historical reenactments.
Geological facts
Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads and axe heads because of its predictable conchoidal fracture pattern.
Field identification & locations
Identify in the field by its sharp, glass-like edges when broken and its ability to scratch glass. Often found in nodules within limestone or as river-worn cobbles.
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