sedimentary

Chert (Jasper / Flint)

Silicon Dioxide (SiO2)

Hardness 7 on Mohs scale, earthy tan to brown-yellow mottling, dull to vitreous/waxy luster, microcrystalline/cryptocrystalline texture, shell-like (conchoidal) fracture, specific gravity around 2.65

Identified July 25, 2026More sedimentary →

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Physical properties

Hardness 7 on Mohs scale, earthy tan to brown-yellow mottling, dull to vitreous/waxy luster, microcrystalline/cryptocrystalline texture, shell-like (conchoidal) fracture, specific gravity around 2.65

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from chemical fluids in sedimentary marine or lake environments, often replacing original limestone or dolomite beds.

Uses & applications

Historically used for stone tools, arrowheads, and spark-striking flints due to its hardness and sharp conchoidal fracturing. Modern usage includes road aggregate, landscaping stone, and lapidary tumbling.

Geological facts

Chert is so fine-grained that its individual quartz crystals cannot be seen without an electron microscope. Native Americans favored high-quality chert and jasper for crafting projectile points.

Field identification & locations

Look for a smooth, glass-like fracture surface with sharp edges when broken, along with a high hardness that easily scratches steel and glass. Extremely common in limestone terrains, gravel beds, and river basins worldwide.