sedimentary

Chert (Flint)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy or dull; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, or gray
Luster: Waxy or dull

Identified May 9, 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: Tan, brown, or gray; Luster: Waxy or dull; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of siliceous remains of marine organisms or through chemical precipitation from silica-rich groundwater within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires; currently used as road aggregate, architectural stone, and sometimes as semi-precious gemstones.

Geological facts

Chert is so hard it can scratch steel. When struck against iron or steel, it produces sparks, which led to its extensive use in flintlock firearms and early fire-making kits.

Field identification & locations

Identify in the field by its smooth, waxy surface and conchoidal (shell-like) fractures with sharp edges. It is commonly found as nodules in limestone or as seafloor deposits.