sedimentary
Flint
SiO2 (Cryptocrystalline Quartz / Chert)
Hardness of 7 on the Mohs scale, dark gray to black exterior with a weathered patina and lighter spots, waxy to vitreous luster, conchoidal fracture, and amorphous or microcrystalline crystal structure.
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Physical properties
Hardness of 7 on the Mohs scale, dark gray to black exterior with a weathered patina and lighter spots, waxy to vitreous luster, conchoidal fracture, and amorphous or microcrystalline crystal structure.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in chalk or limestone by silica-rich solutions in marine environments during the Cretaceous period.
Uses & applications
Historically used for making stone tools, weapons, and fire-starting (strike-a-light). Currently used in decorative landscaping, construction aggregate, and occasionally in knapping hobbies.
Geological facts
Flint is a variety of chert specifically found in chalk formations. It produces sparks when struck against steel due to its high hardness and microcrystalline structure.
Field identification & locations
Easily identified by its distinctive conchoidal fracture, waxy luster, and association with chalk cliffs or coastal pebble beaches. Common worldwide.
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