sedimentary
Chert
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: tan/brown/gray, Luster: dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan/brown/gray, Luster: dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or groundwater precipitation in limestone or chalk beds. Often Paleozoic or Mesozoic in age.
Uses & applications
Historically used for stone tools (flintknapping); currently used in road construction, as a building material, and for geological study.
Geological facts
Chert often contains microfossils. Varieties like jasper and flint are chemically identical but differ in color and formation environment.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and sharp edge when broken. Commonly found in riverbeds and limestone outcrops.
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