sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Brown outer cortex with dark gray/black interior, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown outer cortex with dark gray/black interior, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds. Most common in Cretaceous and Paleozoic strata.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road surfacing, jewelry (as jasper/agate varieties), and as a gemstone when polished.
Geological facts
Flint was one of the first materials traded by prehistoric humans. When struck against steel or pyrite, it produces sparks used to ignite fires or gunpowder in flintlock firearms.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture edges that are sharp as glass, and its ability to scratch glass. Commonly found in riverbeds, chalk cliffs, and limestone quarries.
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