sedimentary

Chert / Flint

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, white with yellow iron staining; Luster: Waxy to dull; Breakage: Conchoidal fracture; Grain: Cryptocrystalline

Hardness: 6
Color: Gray, tan, white with yellow iron staining
Luster: Waxy to dull

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, white with yellow iron staining; Luster: Waxy to dull; Breakage: Conchoidal fracture; Grain: Cryptocrystalline

Formation & geological history

Formed as chemical precipitates or through the replacement of limestone. They often originate as silica-rich fluids filling cavities or replacing organic material in sedimentary basins.

Uses & applications

Historically used for stone tools/weapons (knapping) and making fire. Modernly used in road construction, gravel, and occasionally as an abrasive.

Geological facts

Chert is so tough that it was the primary material for arrowheads and spear points for thousands of years. It can sparks when struck against steel, which led to the name 'flint'.

Field identification & locations

Identify by its extremely smooth, glass-like fracture surfaces and ability to scratch glass. Commonly found as nodules in limestone or as smooth river pebbles.