sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness 7 on Mohs scale; color varies from grey, blue-grey, to brown; waxy to dull luster; conchoidal fracture which creates sharp edges; very dense and non-porous.
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Physical properties
Hardness 7 on Mohs scale; color varies from grey, blue-grey, to brown; waxy to dull luster; conchoidal fracture which creates sharp edges; very dense and non-porous.
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through chemical precipitation in marine or groundwater environments. Can be found in nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used as road aggregate, in glass making, and as a starting material for sparking fire (flint and steel).
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be shaped into extremely sharp tools. It is chemically very stable and resistant to weathering.
Field identification & locations
Look for a smooth, waxy texture and curved, bowl-shaped (conchoidal) fractures. It will easily scratch glass and cannot be scratched by a steel knife. Common in riverbeds and limestone outcrops.
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