sedimentary

Dark flint or chert fragment

Microcrystalline quartz (SiO₂), commonly called flint when dark and nodular

AI-generated identification · may be incorrect

Very fine-grained, gray-black, dull to waxy luster with conchoidal fracture; Mohs hardness about 6.5–7, no cleavage, specific gravity roughly 2.6. The image is insufficient to distinguish flint from other dark chert or possibly weathered volcanic rock with certainty.

Identified August 10, 2026More sedimentary →

Explore Dark flint or chert fragment in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or precipitates within marine limestone, chalk, or other sediments, commonly during the Cretaceous or younger. It occurs as nodules, beds, or broken fragments.

Uses & applications

Historically used for sharp stone tools and fire-starting; today mainly collected, studied, or used decoratively and occasionally as aggregate.

Geological facts

Fresh fractures are typically sharply curved and glass-like, producing very keen edges. Flint and chert are varieties of cryptocrystalline quartz rather than ordinary glass.

Field identification & locations

Common in limestone and chalk regions worldwide, including England, France, the Great Plains, and coastal sedimentary terrains. Test for hardness against glass and inspect a fresh edge; acid reaction would suggest carbonate contamination, not quartz.