$Flint (chert) with a conchoidal fracture (Microcrystalline quartz (SiO₂), commonly called flint when dark-colored) — sedimentary$

sedimentary

Flint (chert) with a conchoidal fracture

Microcrystalline quartz (SiO₂), commonly called flint when dark-colored

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark gray to black, dull to slightly waxy luster, and no visible crystals or cleavage. The sharp, curved fracture surface is characteristic of conchoidal fracture.

Identified October 1, 2026More sedimentary →

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Physical properties

Hardness about 7 Mohs; dark gray to black, dull to slightly waxy luster, and no visible crystals or cleavage. The sharp, curved fracture surface is characteristic of conchoidal fracture.

Formation & geological history

Forms when silica precipitates or replaces material in sedimentary rocks, often as nodules in chalk or limestone. Its age depends on the host deposit; many flints formed during the Cretaceous Period.

Uses & applications

Historically used for stone tools and fire-starting; today collected and occasionally used in decorative stonework.

Geological facts

Flint can break into exceptionally sharp edges, making it valuable to prehistoric toolmakers.

Field identification & locations

The specimen appears to be dark flint fractured from a tan, weathered host rock. Look for a very hard, fine-grained surface and curved fracture ripples; flint occurs widely in chalk and limestone regions.