sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically grey, white, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure with conchoidal fracture, and specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically grey, white, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure with conchoidal fracture, and specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of marine organisms like diatoms and radiolarians, typically in deep marine environments over millions of years.
Uses & applications
Historically used for making stone tools such as arrowheads and knives due to its sharp conchoidal fracture; occasionally used in decorative landscaping or lapidary work.
Geological facts
Chert has been utilized by humans for hundreds of thousands of years to create sharp-edged cutting tools and weapons. Varieties include flint, jasper, and chalcedony.
Field identification & locations
Can be identified in the field by its hardness (scratches glass), waxy luster, and characteristic conchoidal (shell-like) fracture. Commonly found in limestone and chalk formations worldwide.
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