sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: Gray, tan, or black with white outer cortex, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Gray, tan, or black with white outer cortex, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous in age.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road construction, as architectural stone, and for decorative lapidary work.
Geological facts
Flint is a variety of chert that was the most important raw material for early humans to create sharp-edged tools like arrowheads and knives due to its predictable conchoidal fracturing.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Often found as nodules within limestone or as rounded river cobbles.
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