sedimentary
Chert (Flinty variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the replacement of limestone or from the accumulation of silica-rich organic debris (like diatoms or radiolarians) in marine environments. Often found as nodules or bedded deposits within carbonate rocks.
Uses & applications
Historically used for stone tools and starting fires; currently used as a raw material in road construction, as an abrasive, and by hobbyists for flintknapping.
Geological facts
Flint is a variety of chert that has been used by humans since the Stone Age. It produces sharp edges when struck, making it one of the most important minerals in human history for toolmaking.
Field identification & locations
Identify by its characteristic conchoidal fracture (smooth, curved breaks) and its ability to scratch glass. Found globally in limestone and chalk beds, particularly in the UK, USA, and France.
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