sedimentary
Flint
SiO2 (Cryptocrystalline Quartz)
Hardness of 7 on the Mohs scale, typically dark gray, black, brown, or grayish-white, waxy to vitreous luster, amorphous crystal structure with conchoidal fracture, no cleavage, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically dark gray, black, brown, or grayish-white, waxy to vitreous luster, amorphous crystal structure with conchoidal fracture, no cleavage, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions in marine environments over millions of years during the Cretaceous and other periods.
Uses & applications
Historically used for making stone tools, arrowheads, and striking fire with steel. Today used for decorative landscaping, road aggregate, and historically in ball mills.
Geological facts
Flint is virtually identical to chert chemically, but the term flint is traditionally used for varieties found in chalk formations. It fractures with extremely sharp edges, making it ideal for ancient weaponry.
Field identification & locations
Easily identified by its conchoidal fracture, waxy luster, and ability to spark when struck with steel. Commonly found nodules embedded in chalk and limestone cliffs or riverbeds worldwide.
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