sedimentary

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs). Color: Dark brown to blackish with olive/yellow undertones. Luster: Dull to waxy. Crystal Structure: Trigonal/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: Approximately 2.65.

Hardness: 6
Color: Dark brown to blackish with olive/yellow undertones
Luster: Dull to waxy

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians) or by the precipitation of silica from groundwater replacing organic matter. Often associated with limestone/chalk beds or river gravels; can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for stone tools (arrowheads/knapping) due to sharp edges; used today as a decorative landscape stone, abrasive, or in the manufacturing of glass and ceramics.

Geological facts

Chert is so hard it can strike sparks from steel, which led to the name 'flint' being used for lighting fires and early firearms. It is incredibly durable and can survive millions of years in riverbeds.

Field identification & locations

Identify in the field by its smooth, waxy feel and shell-like (conchoidal) fracture when broken. It cannot be scratched by a steel knife. Common in riverbanks and limestone outcroppings.

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