sedimentary

Chert

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray to brown; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline; Specific Gravity: 2.6-2.7.

Hardness: 7 (Mohs scale)
Color: Gray to brown
Luster: Waxy to dull

Identified July 6, 2026More sedimentary →

Explore Chert 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: Gray to brown; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline; Specific Gravity: 2.6-2.7.

Formation & geological history

Formed by the precipitation of silica from aqueous solutions, often as nodules in limestone or chalk, or as bedded deposits from the accumulation of siliceous organic remains like diatoms or radiolarians.

Uses & applications

Used in ancient times for stone tools (knapping) due to its sharp edges; used today as road surfacing material and in jewelry as decorative stones.

Geological facts

Chert and its variety, flint, were among the most important materials for early humans to create spearheads and arrowheads. It can spark when struck against steel.

Field identification & locations

Identify by its smooth, waxy surface and shell-shaped (conchoidal) fractures. It is commonly found in sedimentary basins and limestone outcrops worldwide.