sedimentary

Chert (specifically Black Chert or Flint)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Black to dark grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Black to dark grey
Luster: Waxy to vitreous

Identified June 30, 2026More sedimentary →

Explore Chert (specifically Black Chert or 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 (Mohs scale); Color: Black to dark grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from silica-rich fluids in sedimentary basins. Primarily found in limestone or chalk beds.

Uses & applications

Used historically for stone tools and weapons (arrowheads, scrapers); currently used in road construction, as jewelry (when patterned), and occasionally in start-fire kits.

Geological facts

Chert was one of the most important raw materials for early humans because of its ability to be knapped into sharp edges. Flint is a specific variety of chert often found in chalk.

Field identification & locations

Identify in the field by its characteristic shell-like (conchoidal) fracture pattern and its ability to scratch glass. It is commonly found in nodules within limestone or as pebbles in stream beds.