sedimentary
Chert / Flint
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically white, grey, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with very sharp edges, and specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, grey, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with very sharp edges, and specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from seawater, often replacing carbonate rocks like limestone during diagenesis. Can range widely in geological age from Precambrian to Cenozoic.
Uses & applications
Historically used by early humans for stone tools, arrowheads, and fire-starting (striking against steel). Modern uses include abrasive grit, road aggregate, and historically in flintlock firearms.
Geological facts
Chert and flint are essentially the same material; 'flint' usually refers to dark variations found in chalk deposits, while 'chert' refers to lighter varieties found in limestone.
Field identification & locations
Easily identified by its distinctive conchoidal fracture, sharp edges when broken, and scratching glass easily due to its high quartz hardness. Commonly found globally within limestone and chalk formations.
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