sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

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

Identified May 16, 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 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. Prevalent in limestone and chalk deposits.

Uses & applications

Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a refractory material.

Geological facts

Because it breaks with a conchoidal fracture, it was the primary material for arrowheads and spear points in the Stone Age. It is chemically identical to quartz but with a much finer grain.

Field identification & locations

Identify by its waxy texture and sharp, shell-like (conchoidal) edges when broken. It will scratch glass easily. Commonly found in riverbeds or as nodules within limestone layers.