sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Grey, white, tan, and reddish-brown iron oxide staining. Luster: Waxy to vitreous. Fracture: Distinctive sharp conchoidal fracture. Microcrystalline structure.

Hardness: 7 on Mohs scale
Color: Grey, white, tan, and reddish-brown iron oxide staining
Luster: Waxy to vitreous

Identified July 25, 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: Grey, white, tan, and reddish-brown iron oxide staining. Luster: Waxy to vitreous. Fracture: Distinctive sharp conchoidal fracture. Microcrystalline structure.

Formation & geological history

Formed in marine sedimentary environments from the accumulation of silica-rich biogenic material (such as radiolarian or diatom oozes) or inorganic precipitation of silica within limestone or chalk beds.

Uses & applications

Historically used for knapping sharp stone tools, arrowheads, and spark generation in flintlock firearms. Modernly used as gravel, road base, and by lapidary hobbyists.

Geological facts

Flint and chert produce sparks when struck against iron or steel, making them essential survival tools throughout human history. The sharp edge created by conchoidal fracture can be sharper than a surgical scalpel.

Field identification & locations

Identified in the field by its high hardness (scratches glass), waxy luster, smooth surface texture, and shell-like curved (conchoidal) fractures with sharp edges. Commonly found in limestone and chalk formations worldwide.