sedimentary
Chert (often called Flint or Jasper based on color)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs/scratches glass), Color: Opaque grayish-green/teal, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 – 2.65
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Physical properties
Hardness: 7 (Mohs/scratches glass), Color: Opaque grayish-green/teal, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 – 2.65
Formation & geological history
Formed from the accumulation of microscopic silica shells (radiolarians or diatoms) on the seafloor or by the replacement of carbonate rocks by silica-rich fluids. Can date from the Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and arrowheads. Currently used in road surfacing, as grinding media in ball mills, and occasionally in jewelry as a cabochon.
Geological facts
Because it breaks with a conchoidal fracture like glass, it creates razor-sharp edges. It was one of the most vital materials for early humans to create tools and spark fire.
Field identification & locations
Identify by its waxy texture and shell-like (conchoidal) breaking pattern. It cannot be scratched by a steel knife. Commonly found in riverbeds or within limestone and chalk deposits.
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