sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-grey/tan, Luster: Waxy to dull, Crystal structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-grey/tan, Luster: Waxy to dull, Crystal structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when fractured. Modern uses include road surfacing, decorative landscaping, and occasionally as an ornamental stone.
Geological facts
Chert is so durable that it often survives as pebbles in stream beds long after the surrounding rock has weathered away. It is one of the most common materials used by prehistoric humans for knapping arrowheads.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and coastal regions.
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