sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: White, cream, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: White, cream, tan
Luster: Waxy to dull

Identified July 13, 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: White, cream, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed as nodules or layered deposits in sedimentary rocks (like limestone) through the accumulation of silica-rich organic remains or chemical precipitation. Most deposits range from Paleozoic to Cenozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Today used in road construction, as a flint-striker for fire-making, and occasionally for lapidary work.

Geological facts

Chert has a conchoidal fracture which creates sharp edges, making it the primary material for prehistoric tools. The white variety seen here is often called 'common chert'.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy texture, and sharp, shell-like fracture patterns. Often found in riverbeds or weathered out of limestone cliffs.