sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, brown, tan, and yellowish; Luster: Waxy to dull; Crystal structure: Microcrystalline or cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, brown, tan, and yellowish
Luster: Waxy to dull

Identified May 10, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed in marine environments through the precipitation of silica from seawater or the accumulation of siliceous skeletal remains of organisms like diatoms and radiolaria. Found throughout geological history from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction as road stone, in high-end ceramics, and as decorative gravel. Polished specimens are used in jewelry and lapidary art.

Geological facts

Chert is essentially the same mineral as quartz but with a microscopic crystal structure. Because it breaks with very sharp edges (conchoidal fracture), it was the primary material for prehistoric arrowheads and spear tips.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy feel, and characteristic curved, shell-like fracture marks. Commonly found as nodules in limestone or chalk beds.