sedimentary

Chert (Flint)

Microcrystalline Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91

Hardness: 6
Color: Brown, tan, or grey
Luster: Waxy to dull

Identified May 26, 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: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone/chalk beds. It can date from almost any geological era.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as grinding media, and as a low-cost gemstone for jewelry.

Geological facts

Chert has been used by humans for millions of years due to its ability to break into sharp edges. It is also known as flint when it occurs in chalk or marly limestone.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel), waxy appearance, and characteristic shell-like (conchoidal) fracture edges. Commonly found in riverbeds or as nodules in limestone.