sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale; colors vary from white, gray, brown, to black; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; colors vary from white, gray, brown, to black; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the accumulation of siliceous skeletal remains of marine organisms like radiolaria and diatoms or through the chemical replacement of limestone by silica-rich groundwaters in marine environments.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-striking implements; occasionally used in decorative landscaping and as an abrasive.
Geological facts
Chert has been utilized by humans for hundreds of thousands of years due to its ability to fracture conchoidally into extremely sharp edges, making it ideal for primitive weaponry.
Field identification & locations
Easily identified by its extreme hardness (scratches glass), waxy luster, and smooth conchoidal fracture surfaces. Commonly found embedded in chalk or limestone formations worldwide.
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