sedimentary

Chert (variations include Flint or Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically white, gray, or tan
Luster: waxy to dull

Identified March 16, 2026More sedimentary →

Explore Chert (variations include Flint or Jasper) 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 through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. It is found in geologic strata from the Precambrian to the present, often occurring as nodules or beds within limestone or chalk.

Uses & applications

Historically used for making sharp stone tools and weapons (arrowheads, scrapers). Modern uses include road surfacing, construction aggregate, and occasionally as a gemstone (Jasper) in jewelry. It is also a source of flint for fire-starting.

Geological facts

Chert is so hard it can scratch steel. Because it breaks with a conchoidal fracture like glass, it creates edges that can be sharper than a surgical scalpel. It was one of the most vital materials for prehistoric technology.

Field identification & locations

Identify in the field by its hardness (it should easily scratch glass), its waxy feel, and the distinctive curved 'conchoidal' chips where it has been struck. Commonly found in riverbeds, glacial deposits, and embedded in limestone outcrops.