sedimentary
Flint
SiO2 (Cryptocrystalline Quartz)
Hardness of 7 on the Mohs scale; dark brown, gray, or black color with a lighter weathered cortex; waxy to vitreous luster; microcrystalline structure; conchoidal fracture with very sharp edges; specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; dark brown, gray, or black color with a lighter weathered cortex; waxy to vitreous luster; microcrystalline structure; conchoidal fracture with very sharp edges; specific gravity of 2.60 to 2.65.
Formation & geological history
Forms by the replacement of calcium carbonate by silica-rich solutions in chalk or limestone formations during the Cretaceous period and other sedimentary environments.
Uses & applications
Historically used for making stone tools, arrowheads, and blades, as well as for striking sparks to make fire; modern uses include landscaping, aggregates, and ornamental display.
Geological facts
Flint was one of the most vital materials for early human survival, prized for its ability to fracture conchoidally into razor-sharp edges.
Field identification & locations
Easily identified by its conchoidal fracture, waxy luster, and high hardness (scratches glass). Commonly found as nodules within chalk or limestone deposits worldwide.
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