sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grayish-brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grayish-brown
Luster: Dull to waxy

Identified April 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 on Mohs scale; Color: Grayish-brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in limestone or chalk through a chemical process where silica replaces carbonate materials, often during diagenesis in marine environments.

Uses & applications

Historically used for stone tools and starting fires; currently used as construction aggregate, road surfacing, and occasionally for lapidary work.

Geological facts

Chert's conchoidal fracture produces extremely sharp edges, which made it the primary material for arrowheads and spear points for thousands of years throughout human history.

Field identification & locations

Identify by its extreme hardness (will scratch glass), waxy feel, and characteristic curved (conchoidal) breaks. Extremely common in stream beds and areas with limestone outcrops.