sedimentary

Chert (Chert / Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale. Color: Brown, tan, or grey. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Brown, tan, or grey
Luster: Waxy to vitreous

Identified March 17, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 on the Mohs scale. Color: Brown, tan, or grey. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or by chemical precipitation in marine environments. It can also form by the replacement of limestone or chalk by silica-rich fluids.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal edges. Currently used as road surfacing material, construction aggregate, and occasionally for decorative stone or knapping art.

Geological facts

Dark-colored chert is often called 'Flint.' It was one of the most important minerals to prehistoric humans because it creates hot sparks when struck against steel or pyrite, and it can be flaked into incredibly sharp edges.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and the fact that it will easily scratch glass. Commonly found in limestone beds or as nodules in chalk and stream beds. Collectors look for unique colors or fossil inclusions.