sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Hardness of 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, colors range from white, grey, brown to yellow due to impurities, specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, colors range from white, grey, brown to yellow due to impurities, specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions, often replacing carbonate rocks like limestone during diagenesis, or from the accumulation of siliceous skeletal remains of marine organisms such as radiolarians and diatoms.
Uses & applications
Historically used for making stone tools, arrowheads, and striking fire. Used today in decorative landscaping, road construction, and occasionally in lapidary work.
Geological facts
Chert is a tough, extremely durable sedimentary rock that weathers very slowly, often remaining as residual pebbles in soils and stream beds long after the surrounding limestone has eroded away.
Field identification & locations
Can be identified in the field by its distinct conchoidal fracture (smooth, curved breakage patterns), hardness that can easily scratch glass, and dull to waxy luster. Common worldwide in sedimentary sequences containing limestone or chalk.
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