sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically gray, brown, black, or white in color, waxy to vitreous luster, amorphous or cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically gray, brown, black, or white in color, waxy to vitreous luster, amorphous or cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions, often derived from the skeletal remains of marine organisms like diatoms or radiolarians, accumulating in carbonate or clay-rich sediments over millions of years.
Uses & applications
Historically used by ancient humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Also used historically for striking fire.
Geological facts
Chert is extremely durable and weather-resistant, which is why ancient stone tools made from it survive exceptionally well in the archaeological record. Varieties include flint, jasper, and chalcedony.
Field identification & locations
Can be identified in the field by its sharp, curved (conchoidal) fracture edges, waxy luster, and high hardness (it will easily scratch glass). Found globally in limestone and other sedimentary rock formations.
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