sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, tan, and brown with white inclusions; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray, tan, and brown with white inclusions
Luster: Dull to waxy

Identified March 29, 2026More sedimentary →

Explore Chert (Nodule) 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 diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.

Uses & applications

Historically used for stone tools and weapons. Currently used in road surfacing, construction aggregate, and occasionally as lapidary material for tumbling or cabochons.

Geological facts

Chert is so hard it can scratch steel and produce sparks when struck against iron, a property that led to its widespread use in flintlock firearms. When it is high-quality and colorful, it is often called Jasper.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules or layers within sedimentary rock outcrops like limestone.