sedimentary
Chert (Flint variety)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to charcoal, 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: Dark grey to charcoal, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used in construction aggregate, as gemstones when colorful, and in flintlock mechanisms.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its use in early firearms; it is also one of the first materials ever mined by prehistoric humans.
Field identification & locations
Identify by its waxy texture and sharp, curved (conchoidal) edges when broken. Commonly found in nodular form within limestone outcrops or as river cobbles.
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