sedimentary
Flint
Silicon dioxide (SiO2) - cryptocrystalline quartz
Hardness of 7 on the Mohs scale; varies in color from grey, white, brown, to black; waxy to vitreous luster; microcrystalline/cryptocrystalline structure; no cleavage, exhibits characteristic conchoidal fracture; specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; varies in color from grey, white, brown, to black; waxy to vitreous luster; microcrystalline/cryptocrystalline structure; no cleavage, exhibits characteristic conchoidal fracture; specific gravity around 2.60 to 2.65.
Formation & geological history
Forms by the replacement of calcium carbonate by silica-rich solutions in sedimentary environments, typically as nodules within chalk or limestone formations during the Cretaceous period.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-striking fire starters; currently used in abrasives, ceramics, and as a decorative stone.
Geological facts
Flint was one of the earliest materials manipulated by early humans to create cutting tools and weapons due to its predictable conchoidal fracture when struck.
Field identification & locations
Identified easily by its conchoidal fracture, sharp edges when broken, waxy luster, and association with chalk or limestone deposits. Commonly found globally wherever chalk cliffs or limestone strata occur.
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