sedimentary

Chert (Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits prominent conchoidal fracture); Specific gravity: 2.6 – 2.7

Hardness: 7 on Mohs scale
Color: Gray, tan, and brownish with distinct banding
Luster: Waxy to dull

Identified April 10, 2026More sedimentary →

Explore Chert (Flint variety) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments. This specimen appears to be a nodule or fragment found in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and to start fires (striking steel). Modernly used as a decorative stone, in construction aggregate, and occasionally in jewelry as polished stones.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most vital resources for prehistoric humans globally due to its predictable breaking pattern (conchoidal fracture) which produces razor-sharp edges.

Field identification & locations

Identify by its 'flinty' waxy look and shell-like (conchoidal) breaks. Often found as nodules within limestone or along riverbeds where the harder chert has outlasted the surrounding softer rock. It will spark when struck against carbon steel.