sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Grey, tan, and creamy white, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Grey, tan, and creamy white, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed as nodules in limestone or chalk through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation. Most are from the Cretaceous or older geological periods.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Today used in landscaping, as a road base material, and occasionally for primitive fire-starting and jewelry.
Geological facts
Flint was one of the most important resources for prehistoric humans. When struck, it breaks with sharp edges suitable for cutting. It is famous for producing sparks when struck against steel.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or eroded out of limestone cliffs.
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