sedimentary
Flint (or Chert)
Microcrystalline Quartz (SiO2)
Hardness of 7 on the Mohs scale; color typically dark grey, black, brown, or white; waxy to vitreous luster; cryptocrystalline 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; color typically dark grey, black, brown, or white; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity of 2.60 to 2.65.
Formation & geological history
Formed as nodules or concretions in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions in marine environments, often during the Cretaceous period.
Uses & applications
Historically used for prehistoric stone tools, weapons, and fire-starting (strike-a-light). Modern uses include landscaping, decorative gravel, abrasive milling, and occasionally lapidary work.
Geological facts
Flint was one of the earliest materials manipulated by early humans to create advanced tools due to its predictable conchoidal fracture, which allows it to be shaped into extremely sharp edges through knapping.
Field identification & locations
Can be identified in the field by its waxy luster, conchoidal fracture pattern, dark weathering rind, and high hardness capable of scratching glass and producing sparks with steel. Found worldwide in chalk and limestone deposits.
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