sedimentary
Flint (Chert Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Dark grey to brown with a white chalky cortex, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal (produces sharp edges)
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Physical properties
Hardness: 7 (Mohs), Color: Dark grey to brown with a white chalky cortex, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal (produces sharp edges)
Formation & geological history
Formed as nodules within sedimentary rocks like chalk or limestone by the replacement of calcium carbonate with silica, typically in marine environments during the Cretaceous period
Uses & applications
Historically used for making stone tools (knapping) and starting fires; currently used in jewelry, road construction, and as a collector specimen
Geological facts
Flint was one of the most important materials in human history, allowing prehistoric people to create sharp tools and weapons. Its ability to create sparks when struck against steel is due to tiny particles of iron being shaved off and igniting in the air.
Field identification & locations
Identified by its conchoidal fracture which creates razor-sharp edges and its often rough, white outer 'cortex.' Often found in chalk cliffs or as pebbles on beaches in the UK and Europe.
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