sedimentary
Flint Nodule
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey/brown with waxy luster, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey/brown with waxy luster, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed as nodules or concretions in limestone or chalk beds, typically through the chemical replacement of calcium carbonate by silica-rich fluids during diagenesis in the Cretaceous period (approx. 66-145 million years ago).
Uses & applications
Historically used for stone tools and firearms (flintlocks); currently used as a grinding medium in ball mills, in road construction, and for primitive fire-starting demonstrations.
Geological facts
Flint was one of the most important minerals for prehistoric humans due to its ability to split into thin, razor-sharp edges. It is often found with a white exterior 'rind' called a cortex.
Field identification & locations
Identify by its bumpy, irregular nodular shape, waxy appearance when wet, and sharp, shell-like (conchoidal) fractures if broken. Common on beaches in the UK, France, and parts of the USA.
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