sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Smoky grey to black, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Smoky grey to black, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed as nodules or beds in limestone or chalk through the accumulation of siliceous remains of marine organisms or chemical precipitation of silica from groundwater.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and as fire-starters; currently used in gravel, road construction, and as decorative landscape stone.
Geological facts
Dark-colored chert is often specifically called flint. It was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges.
Field identification & locations
Look for a smooth, waxy texture and shell-like (conchoidal) fractures when broken. Commonly found in riverbeds, limestone outcrops, and coastal cliffs.
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