sedimentary
Chert (Flint)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black with tan/white cortex, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black with tan/white cortex, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone. This specimen shows a distinctive white weathered cortex common in nodules found in chalk or limestone beds.
Uses & applications
Historically used for stone tools (knapping) and starting fires. Modern uses include road surfacing, jewelry as 'striped flint', and historical artifact replicas.
Geological facts
Flint is a specific variety of chert often associated with chalk or marly limestone. It was the primary material for the Stone Age technology due to its predictable conchoidal fracture which creates razor-sharp edges.
Field identification & locations
Identified by its extremely smooth, glass-like fracture surfaces and a rough, lighter-colored outer skin (cortex). Common in chalk deposits and riverbeds. It can scratch glass easily.
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