sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray to blue-gray with waxy luster; Crystal Structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray to blue-gray with waxy luster

Identified June 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: 7 on Mohs scale; Color: Gray to blue-gray with waxy luster; Crystal Structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.

Formation & geological history

Formed in marine environments through the precipitation of silica or from the remains of silica-rich organisms like radiolarians. Often occurs as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road construction, landscaping, and as an abrasive in some industrial processes.

Geological facts

Flint is a variety of chert that produced sparks when struck against steel, which made it vital for early firearms (flintlocks) and fire-making. It breaks into edges sharper than a steel scalpel.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy feel, and characteristic curved (conchoidal) breaks. Look for it in limestone outcrops or as rounded pebbles in stream beds.