sedimentary

Chert / Flint

Cryptocrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically brown, grey, white, or black in color, waxy to vitreous luster, conchoidal fracture with no true cleavage, and a specific gravity around 2.60 to 2.65.

Identified July 28, 2026More sedimentary →

Explore Chert / Flint 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 brown, grey, white, or black in color, waxy to vitreous luster, conchoidal fracture with no true cleavage, and a specific gravity around 2.60 to 2.65.

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of microscopic marine organisms (like radiolarians and diatoms) within carbonate sedimentary environments, primarily limestone or chalk, over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting (flint and steel); currently used in abrasive products, road aggregate, and occasionally in decorative landscaping.

Geological facts

Chert is extremely durable and weather-resistant, which is why prehistoric stone tools made from it survive intact for hundreds of thousands of years. Varieties heavily pigmented with dark organic matter or iron oxides are often specifically called flint.

Field identification & locations

Identified easily by its distinctive conchoidal fracture (curved, sharp glass-like breaking patterns) and high hardness that readily scratches glass and steel. Commonly found weathering out of chalk or limestone formations worldwide.