sedimentary

Chert (Flint variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 14, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and as a strike-a-light to start fires. Modernly used in road construction, as jewelry (when patterned), and as a gemstone (jasper/agate varieties).

Geological facts

Chert was one of the most important minerals for early human survival due to its ability to produce sharp edges when fractured. It is highly resistant to chemical weathering.

Field identification & locations

Identify by its very sharp, curved (conchoidal) edges when broken and its ability to scratch glass. Commonly found as nodules or layers within sedimentary limestone formations.