sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, dull to waxy luster, conchoidal fracture, crypto-crystalline structure, colors range widely from white and grey to brown and black due to impurities.
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Physical properties
Hardness of 7 on the Mohs scale, dull to waxy luster, conchoidal fracture, crypto-crystalline structure, colors range widely from white and grey to brown and black due to impurities.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions, often originating from the accumulation of siliceous skeletal remains of marine organisms like radiolarians or diatoms in deep marine environments over millions of years.
Uses & applications
Historically used by early humans for making stone tools (such as arrowheads and spear points due to its conchoidal fracture), as well as for striking fire. Today used occasionally in road aggregate and abrasive products.
Geological facts
Flint is a well-known variety of chert. It can produce sparks when struck against steel, which made it historically vital for firearm ignition mechanisms (flintlocks).
Field identification & locations
Can be identified in the field by its very hard nature (scratches glass), smooth conchoidal fracture surfaces, and waxy luster. Commonly found embedded in limestone or chalk formations worldwide.
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