sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Brown, tan, and gray waxy tones, Luster: Vitreous to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified July 8, 2026More sedimentary →

Explore Chert (Flint) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale), Color: Brown, tan, and gray waxy tones, Luster: Vitreous to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed in marine or freshwater environments as the result of silica-rich fluids replacing organic matter or precipitating from groundwater. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads and scrapers) due to its sharp edges when broken. Today, used as road aggregate, in jewelry as lapidary material, or as fire-starting flint.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can create sparks, a property that led to its widespread use in flintlock firearms and early fire-making kits.

Field identification & locations

Identify in the field by its smooth, waxy surface and its tendency to break with curved, shell-like (conchoidal) surfaces. It is extremely common in riverbeds and gravel pits globally.