sedimentary

Chert (variations include Flint or Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Identified May 3, 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

Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within sedimentary beds. Found in limestone or chalk deposits throughout many geological eras from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons (arrowheads) due to sharp edges; currently used as a raw material for concrete, road surfacing, and as a polishing abrasive.

Geological facts

Chert was one of the first materials used by prehistoric humans to make fire and sharp-edged tools. Its conchoidal fracture allows it to break into predictable, razor-sharp pieces.

Field identification & locations

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