sedimentary
Chert (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within limestone or chalk beds. Often Mesozoic to Cenozoic in age.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road construction, as an abrasive, and sometimes in jewelry as tumbled stones.
Geological facts
Flint is a variety of chert that was essential to prehistoric humans because it breaks into razor-sharp edges. It produces sparks when struck against steel.
Field identification & locations
Identify by its conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in nodules within limestone formations or as river pebbles.
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