sedimentary
Flint
Cryptocrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically dark gray, black, or dark brown with a waxy to vitreous luster, conchoidal fracture, and no true cleavage.
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Physical properties
Hardness of 7 on the Mohs scale, typically dark gray, black, or dark brown with a waxy to vitreous luster, conchoidal fracture, and no true cleavage.
Formation & geological history
Formed as nodules or masses in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions over millions of years.
Uses & applications
Historically used for making stone tools, weapons, and fire-starting flint-and-steel sets; currently used in decorative landscaping and occasionally in specialized industrial applications.
Geological facts
Flint has been utilized by humans since the Stone Age due to its ability to fracture sharply, creating extremely keen edges known as conchoidal fractures.
Field identification & locations
Easily identified by its dark, often weathered exterior, smooth waxy interior fracture surfaces, conchoidal chipping, and ability to scratch glass.
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