sedimentary

Chert

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness of 7 on the Mohs scale; colors vary widely from white, grey, brown to black; vitreous to waxy luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.

Identified August 3, 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

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions, often derived from the skeletal remains of microscopic marine organisms like diatoms or radiolarians, accumulating on ocean floors over millions of years.

Uses & applications

Historically used by early humans for making stone tools such as arrowheads, spear points, and blades due to its sharp conchoidal fracture. Also used in abrasives and occasionally as a decorative or ornamental stone.

Geological facts

Chert is a very durable and resilient rock that resists weathering better than surrounding limestone formations, often standing out as nodules or layers in eroding cliffs.

Field identification & locations

Identified easily by its extreme hardness (scratches glass), waxy to dull luster, and distinct smooth conchoidal fracture resembling broken glass. Found worldwide in sedimentary sequences, particularly limestone and chalk deposits.