sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Mohs hardness of 7, dark grey to black color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture with sharp edges
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Physical properties
Mohs hardness of 7, dark grey to black color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture with sharp edges
Formation & geological history
Formed in sedimentary marine or lacustrine environments from the accumulation of siliceous organism remains (diatoms, radiolarians) or chemical precipitation of silica
Uses & applications
Historically used for stone tools, arrowheads, and spark ignition; currently used in knapping, road aggregate, and mineral collections
Geological facts
Flint and chert produce a curved, shell-like (conchoidal) fracture pattern when struck, allowing it to break into extremely sharp edges, which made it crucial to ancient human technology
Field identification & locations
Look for microcrystalline texture, lack of visible mineral grains, sharp fracture edges, and high hardness (scratches glass). Commonly found in chalk and limestone formations
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