sedimentary
Chert (or Flint)
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically white, cream, gray, or brown in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, and a specific gravity of around 2.60.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, cream, gray, or brown in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, and a specific gravity of around 2.60.
Formation & geological history
Formed in marine environments through the chemical precipitation of silica from seawater or the replacement of limestone by silica-rich solutions over millions of years.
Uses & applications
Historically used by early humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically for fire-starting.
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.
Field identification & locations
Can be identified in the field by its smooth, waxy luster, hard scratch resistance against steel, and characteristic sharp conchoidal fracture edges. Commonly found embedded in limestone or chalk formations.
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