sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: tan, grey, beige; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: tan, grey, beige
Luster: waxy to dull

Identified July 15, 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: tan, grey, beige; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich microfossils like radiolarians or diatoms. Most common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for stone tools and weapons (arrowheads) due to its sharp edges; currently used as a road base, in construction, and occasionally for flintlock firearms.

Geological facts

Chert has a conchoidal fracture, allowing it to break into razor-sharp edges. It was one of the most important resources for prehistoric humans. The variety known as 'Flint' is specifically found in chalk or marly limestone.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and the way it breaks into curved, shell-like flakes. Found globally in areas with sedimentary limestone outcrops.