sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7.0 (Mohs scale); Color: Gray, brown, tan; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7
Color: Gray, brown, tan
Luster: Waxy to vitreous

Identified June 22, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7.0 (Mohs scale); Color: Gray, brown, tan; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily in marine environments through the accumulation of silica-rich microfossils or precipitation from fluids. It is often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modernly used in construction aggregate, as fire-starting flint, and in gemstone tumbling.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. When struck against steel, it produces sparks used to ignite fire, a property essential to early gunpowder weapons.

Field identification & locations

Identified by its extremely smooth, shell-like (conchoidal) fracture and sharp edges. It is found globally in sedimentary basins. Collectors look for unique banding or translucent properties.