sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 Mohs scale; Color: typically grey, brown, or yellowish-green; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none, shows conchoidal fracture.

Hardness: 7 Mohs scale
Color: typically grey, brown, or yellowish-green
Luster: waxy to dull

Identified June 12, 2026More sedimentary →

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: typically grey, brown, or yellowish-green; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none, shows conchoidal fracture.

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in limestone or chalk beds. Commonly found in Paleozoic to Mesozoic sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and as flint for spark-based fire starting. Today used primarily for landscaping, road ballast, or as a source of high-quality silica for ceramic manufacturing.

Geological facts

Flint is a variety of chert that occurs specifically in chalk or marl. It was one of the first materials ever mined by humans during the Neolithic period. Its ability to produce sparks when struck against steel is due to its high hardness.

Field identification & locations

Identify in the field by its waxy luster, sharp edges, and characteristic 'shell-like' shell fracture. It is common in riverbeds and limestone outcrops. Avoid confusion with obsidian by checking for translucency and parent rock association.