sedimentary
Flint
SiO2 (Cryptocrystalline Quartz / Chert)
Hardness of 7 on the Mohs scale; dark gray, brown, or black color; waxy to vitreous luster; microcrystalline or cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; dark gray, brown, or black color; waxy to vitreous luster; microcrystalline or cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity of 2.60 to 2.65.
Formation & geological history
Formed in marine environments as a replacement of calcium carbonate in chalk or limestone beds by silica-rich solutions. Typically Cretaceous to Jurassic in geological age.
Uses & applications
Historically used for making stone tools, arrowheads, and striking fire; modern uses include landscaping, abrasive grinding balls, and decorative items.
Geological facts
Flint was one of the earliest materials manipulated by early humans to create sharp cutting edges and projectiles due to its predictable conchoidal fracture.
Field identification & locations
Identified by its waxy luster, smooth water-worn exterior, and sharp conchoidal edges. Commonly found in chalk deposits and river gravels worldwide.
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