sedimentary

Chert / Jasper

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Rusty brown to reddish due to iron oxide staining, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal (shell-like curves)

Hardness: 6

Identified July 1, 2026More sedimentary →

Explore Chert / Jasper 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 as a sedimentary rock by the accumulation of silica-rich microfossils (like radiolarians) or through the chemical precipitation of silica in groundwater. This specimen shows significant oxidation (iron staining) from weathering.

Uses & applications

Historically used for stone tools (flint knapping) due to its sharp edges when broken. Modern uses include decorative landscaping, gravel, and occasionally as a lapidary material for polishing.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away, which is why it is frequently found as rounded river stones or rugged nodules in fields.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its sharp, curved fracture lines. It is found globally in limestone and dolomite formations or as alluvial pebbles in stream beds.