sedimentary
Flint
SiO2 (Microcrystalline Quartz / Chert)
Hardness of 7 on the Mohs scale, typically dark grey, black, or brown with a white chalky cortex, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, specific gravity of 2.60-2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically dark grey, black, or brown with a white chalky cortex, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no cleavage, specific gravity of 2.60-2.65.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during the Cretaceous period or other sedimentary environments.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-producing fire starters; currently used in abrasives, ceramics, and as a decorative stone.
Geological facts
Flint produces sparks when struck against steel due to iron micro-particles chipping off and igniting in the air, which made it crucial for early firearms and fire making.
Field identification & locations
Easily identified by its smooth, conchoidal fracture surfaces, dark color, and sharp edges when broken. Frequently found in chalk cliffs, beaches, and river gravels.
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