sedimentary
Flint (Chert)
Silicon Dioxide (SiO2)
Hardness of 7 on the Mohs scale; color typically gray, white, brown, or black; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; color typically gray, white, brown, or black; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity around 2.60 to 2.65.
Formation & geological history
Forms by the replacement of calcium carbonate by silica in marine limestone or chalk during diagenesis, or through the direct precipitation of silica from aqueous solutions. Geological age ranges from Cretaceous to older formations.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting (striking against steel). Also used in construction, road aggregate, and historically in flintlock firearms.
Geological facts
Flint is extremely durable and breaks with a conchoidal fracture that produces razor-sharp edges, making it one of the most important materials for early human toolmaking during the Stone Age.
Field identification & locations
Easily identified in the field by its distinctive white weathered outer cortex, dark interior, waxy luster, and sharp conchoidal edges. Commonly found as nodules within chalk or limestone formations.
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