sedimentary
Chert (White Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: White to light grey, Lustre: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to light grey, Lustre: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils like diatoms or radiolarians, or via chemical precipitation in ocean or lake sediments. It is often found as nodules or layers in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include abrasives, road construction, and as a component in ceramics or glass.
Geological facts
Chert is so hard it can spark when struck against steel. Prehistoric humans highly valued white chert for its ability to hold a sharp edge after being knapped.
Field identification & locations
Identify in the field by its very sharp, curved (conchoidal) fractures and its ability to scratch glass. It is commonly found in sedimentary basins and along riverbeds.
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