sedimentary

Chert (including Flint and Jasper variants)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: variety of grays, blacks, and browns; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: variety of grays, blacks, and browns
Luster: waxy to dull

Identified April 26, 2026More sedimentary →

Explore Chert (including Flint and Jasper variants) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as gemstones when colorful (jasper), and for starting fires (flint).

Geological facts

Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges; it is also highly resistant to chemical weathering.

Field identification & locations

Identify in the field by checking for a smooth, glass-like fracture (conchoidal), high hardness (cannot be scratched by a steel knife), and a waxy texture. Commonly found as nodules in limestone or chalk beds.