sedimentary

Chert (variations include Flint/Jasper)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale). Color: Highly variable (grey, brown, tan). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Highly variable (grey, brown, tan)
Luster: Waxy to dull

Identified March 21, 2026More sedimentary →

Explore Chert (variations include Flint/Jasper) 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 (Mohs scale). Color: Highly variable (grey, brown, tan). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6 – 2.7.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or through chemical precipitation in limestone/chalk beds. They appear as nodules or layered beds in sedimentary formations ranging from Precambrian to Cenozoic ages.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, grinding media, and occasionally as semi-precious gemstones in jewelry (as Jasper).

Geological facts

Chert was one of the most important minerals for early humans because of its predictable conchoidal fracture patterns, allowing it to be 'knapped' into arrowheads and scrapers.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone outcrops or as rounded pebbles in riverbeds.