sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs; Color: Brown to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 Mohs
Color: Brown to dark grey
Luster: Waxy to dull

Identified June 6, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 Mohs; Color: Brown to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. Can vary in age from Precambrian to Cenozoic.

Uses & applications

Used historically for stone tools and starting fires; currently used in construction as aggregate, lapidary arts, and as a raw material for gemstones.

Geological facts

Flint was a crucial material for early humans to create sharp-edged tools and weapons. Its ability to produce sparks when struck against steel made it essential for early firearms (flintlocks).

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and distinctive shell-like (conchoidal) fracture pattern. Commonly found as nodules in limestone or chalk beds.