sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Gray to black, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific Gravity: 2.65
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Physical properties
Hardness: 7 Mohs, Color: Gray to black, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific Gravity: 2.65
Formation & geological history
Formed primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds. Ages range from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, as jewelry (when patterned), and for lapidary work.
Geological facts
Flint is a variety of chert that was essential to human survival during the Stone Age due to its ability to produce sharp edges when struck. It generates sparks when hit against steel.
Field identification & locations
Identify in the field by its smooth, glass-like breakage surfaces (conchoidal fracture), extreme hardness (it will scratch glass), and a waxy texture. Commonly found in riverbeds or eroding out of limestone cliffs.
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