sedimentary
Chert
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 Mohs, Color: tan to yellowish-brown, Luster: waxy to dull, Structure: microcrystalline (no visible grains), Fracture: conchoidal, Specific Gravity: 2.5-2.8
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Physical properties
Hardness: 7 Mohs, Color: tan to yellowish-brown, Luster: waxy to dull, Structure: microcrystalline (no visible grains), Fracture: conchoidal, Specific Gravity: 2.5-2.8
Formation & geological history
Formed in marine or freshwater environments as the result of the accumulation of siliceous oozes or by the replacement of carbonate rocks by silica-rich fluids. Can be billions of years old or relatively recent.
Uses & applications
Used historically for stone tools (knapping) due to its sharp edges; modern uses include construction aggregate, road surfacing, and as a polishing abrasive.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads, scrapers, and blades because it breaks with incredibly sharp edges. It is essentially a gemstone-adjacent material similar to jasper or flint.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy feel, and smooth curved (conchoidal) fracture surfaces. Commonly found in limestone or dolomite beds as nodules or layers.
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