sedimentary
Flint
SiO2 (Microcrystalline Quartz / Chert)
Hardness of 7 on the Mohs scale, colors range from gray, white, brown to black with a characteristic chalky white outer cortex, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from gray, white, brown to black with a characteristic chalky white outer cortex, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed diagenetically through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions derived from sponge spicules or other microfossils, typically during the Cretaceous period.
Uses & applications
Historically used for stone tools, weaponry, and fire-starting (flint and steel); currently used in abrasive grit, road aggregate, and historically in flintlock firearms.
Geological facts
Flint is a hard, sedimentary form of the mineral quartz known for breaking with a sharp conchoidal fracture, making it ideal for ancient tools and weapons.
Field identification & locations
Easily identified in the field by its conchoidal fracture, waxy luster, hardness that scratches glass, and the presence of a soft, chalky white outer weathering crust (cortex). Commonly found embedded in chalk cliffs and beaches.
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