sedimentary
Flint
SiO2 (Cryptocrystalline Quartz / Chert)
Hardness: 7 on the Mohs scale, Color: Dark grey to black or brown, Luster: Vitreous to waxy, Crystal Structure: Microcrystalline / Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.60 - 2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: Dark grey to black or brown, Luster: Vitreous to waxy, Crystal Structure: Microcrystalline / Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.60 - 2.65
Formation & geological history
Forms by the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during diagenesis. Geologically widespread from the Cretaceous period onwards.
Uses & applications
Historically used for making stone tools, arrowheads, and striking fire. Occasionally used in ornamental objects, grinding pebbles, and historical construction.
Geological facts
Flint played a critical role in human history for toolmaking and fire-starting due to its sharp conchoidal fracture when struck.
Field identification & locations
Identified easily by its conchoidal (shell-like) fracture, sharp edges, dark coloration, and hardness that easily scratches glass. Found globally within chalk and limestone formations.
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