sedimentary
Flint / Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, colors range from gray, dark brown, to black, vitreous to waxy luster, cryptocrystalline structure, conchoidal fracture with sharp edges, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from gray, dark brown, to black, vitreous to waxy luster, cryptocrystalline structure, conchoidal fracture with sharp edges, specific gravity of 2.60 to 2.65.
Formation & geological history
Forms by the replacement of calcium carbonate by silica in sedimentary environments such as chalk or limestone deposits, typically during the Cretaceous period or earlier.
Uses & applications
Historically used for making stone tools, weapons, and fire-starting (flint and steel). Currently used in decorative landscaping, abrasive grits, and as historical/archaeological collector specimens.
Geological facts
Flint played a crucial role in human evolution by providing durable cutting edges and a reliable method to create fire. It produces sparks when struck against steel due to tiny embedded iron pyrite crystals or friction-induced heat.
Field identification & locations
Easily identifiable in the field by its distinct conchoidal fracture, waxy luster, and ability to scratch glass. Commonly found nodular within chalk or limestone formations worldwide.
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