sedimentary
Flint
Microcrystalline Quartz (SiO2)
Mohs hardness of 7; colors range from dark gray, brown, to black with a characteristic white chalky outer cortex; 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
Mohs hardness of 7; colors range from dark gray, brown, to black with a characteristic white chalky outer cortex; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; 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 Cretaceous period and other geological epochs.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-striking implements; today mostly found in gravels or used for decorative aggregate.
Geological facts
Flint and chert are essentially the same mineral, though 'flint' typically refers to the dark varieties found specifically in chalk deposits. It was one of the earliest materials manipulated by early humans for technology.
Field identification & locations
Easily identified by its dark, smooth interior, conchoidal fracture, sharp edges when broken, and soft, chalky white outer rind. Found worldwide in chalk cliffs and marine sedimentary layers.
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