sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: dark gray, black, or bluish-gray; Luster: waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: dark gray, black, or bluish-gray
Luster: waxy to dull

Identified July 15, 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

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include construction aggregate, gemstones, and fire-starting kits.

Geological facts

Flint was one of the first materials used by early humans to create fire and sharp tools. It is extremely durable and weather-resistant, often surviving long after the surrounding limestone has eroded.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is common in limestone regions like the central US, UK, and France.