sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically grey, white, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure with conchoidal fracture, and specific gravity around 2.6.

Identified August 5, 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 of 7 on the Mohs scale, typically grey, white, brown, or black in color, waxy to vitreous luster, cryptocrystalline structure with conchoidal fracture, and specific gravity around 2.6.

Formation & geological history

Formed by the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of marine organisms such as radiolarians and diatoms, typically during the Mesozoic and Paleozoic eras.

Uses & applications

Historically used by early humans for making stone tools such as arrowheads and knives due to its conchoidal fracture. Today used in abrasives and occasionally decorative landscaping.

Geological facts

Chert is extremely durable and resistant to weathering, which is why ancient stone tools made from chert survive intact for thousands of years. Varieties include flint and jasper.

Field identification & locations

Can be identified in the field by its sharp conchoidal fracture edges and hardness that easily scratches glass. Commonly found within limestone and chalk formations worldwide.