sedimentary
Flint
Silicon dioxide (SiO2)
Hardness of 7 on the Mohs scale, colors ranging from dark grey, blue, black, to brown and yellowish due to impurities, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, specific gravity of 2.60 to 2.65
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Physical properties
Hardness of 7 on the Mohs scale, colors ranging from dark grey, blue, black, to brown and yellowish due to impurities, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, specific gravity of 2.60 to 2.65
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during the diagenesis of sedimentary rock, typically millions of years old from the Cretaceous period.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-producing fire starters. Currently used in decorative stone, abrasives, and historically in flintlock firearms.
Geological facts
Flint is a hard, sedimentary form of the mineral quartz and is notorious for fracturing in a very sharp, predictable manner (conchoidal fracture), which made it the premier material for prehistoric stone tool manufacture.
Field identification & locations
Easily identified in the field by its conchoidal fracture, waxy luster, ability to scratch glass easily, and its common occurrence as nodules embedded within chalk or limestone formations.
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