sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale. Color: Brown, tan, and gray with waxy luster. Conchoidal fracture (breaks like glass with curved edges). Cryptocrystalline structure. Specific gravity: 2.65.

Hardness: 7 Mohs scale
Color: Brown, tan, and gray with waxy luster

Identified July 14, 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: 7 Mohs scale. Color: Brown, tan, and gray with waxy luster. Conchoidal fracture (breaks like glass with curved edges). Cryptocrystalline structure. Specific gravity: 2.65.

Formation & geological history

Formed in marine environments through the precipitation of silica or the accumulation of silica-rich microfossils like radiolaria. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in landscaping, as a flint for fire-starting, and occasionally as a minor abrasive or for decorative gravel.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the most important raw material for toolmaking throughout the Stone Age due to its predictable breaking pattern and sharp edges.

Field identification & locations

Identify in the field by its smooth, waxy surface and the presence of sharp, curved edges where it has chipped. It will easily scratch glass and will not react to acid. Commonly found in riverbeds and limestone outcrops.