sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Mohs hardness 7. Conchoidal fracture with sharp edges. Dull to waxy or vitreous luster. Color ranges from tan, brown, yellowish-brown to dark gray or black. Microcrystalline structure with very fine texture.
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Physical properties
Mohs hardness 7. Conchoidal fracture with sharp edges. Dull to waxy or vitreous luster. Color ranges from tan, brown, yellowish-brown to dark gray or black. Microcrystalline structure with very fine texture.
Formation & geological history
Formed in marine environment sediments through the accumulation of siliceous oozes or replacement of carbonate rocks (such as limestone) by silica-rich fluids during diagenesis.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-striking flints. Modern uses include construction aggregate and decorative specimens.
Geological facts
Chert and flint have been used by humans for hundreds of thousands of years due to how predictably they fracture, leaving razor-sharp edges ideal for tools.
Field identification & locations
Identified by high hardness (scratches glass), smooth conchoidal fracture surfaces, and fine grain. Very common in limestone and chalk formations worldwide.
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