sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 (Mohs scale), Color: Dark grey to brown, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6

Identified June 7, 2026More sedimentary →

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: Dark grey to brown, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or from chemical precipitation. Commonly found in limestone or chalk beds.

Uses & applications

Used historically for stone tools and weapons (knapping), fire-starting (flint and steel), and currently as an additive in concrete, road base, and for gemstone tumbling/jewelry.

Geological facts

Flint was one of the most important raw materials for early humans; it breaks with sharp conchoidal edges ideal for creating knives and arrowheads.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and ability to scratch glass. Found often as nodules within sedimentary rocks like limestone.