sedimentary
Flint / Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, colors range from grey, brown, white, to yellowish-brown due to impurities, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from grey, brown, white, to yellowish-brown due to impurities, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the diagenesis of siliceous oozes or through the replacement of limestone or chalk by silica-rich groundwater, occurring primarily in marine sedimentary environments over millions of years.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting (flint and steel); modern uses include abrasives, road aggregate, and decorative landscaping or specimens.
Geological facts
Flint is famously known for its razor-sharp conchoidal fracture when struck, which made it the premier material for prehistoric stone tool technology across the globe.
Field identification & locations
Easily identified by its conchoidal fracture, waxy luster, and ability to scratch glass (hardness 7). Frequently found as nodules in chalk or limestone formations and weathered river gravels or beaches.
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