sedimentary

Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or white
Luster: Waxy to dull

Identified June 29, 2026More sedimentary →

Explore Chert 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 on Mohs scale; Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed in marine environments through the accumulation of siliceous remains of organisms like diatoms and radiolarians, or through chemical precipitation in limestone or chalk beds. Commonly found in Paleozoic and Mesozoic sedimentary strata.

Uses & applications

Historically used for stone tools such as arrowheads due to its sharp edges when broken. Today used as road gravel, construction aggregate, and occasionally as a minor gemstone (jasper/agate varieties).

Geological facts

Chert is so hard it can scratch glass and sparks when struck against steel. It was one of the most vital materials for early humans to create survival tools.

Field identification & locations

Identify by its smooth, waxy feel and shell-like (conchoidal) fracture patterns. Frequently found in riverbeds or as nodules within limestone outcrops.