sedimentary

Chert (Jasper/Agate variety)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Waxy orange, yellow, and brown; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Waxy orange, yellow, and brown
Luster: Vitreous to waxy

Identified June 19, 2026More sedimentary →

Explore Chert (Jasper/Agate 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 microfossils or chemical precipitation in sedimentary basins. The silica often replaces other minerals or fills voids in host rock over millions of years.

Uses & applications

Predominantly used for lapidary work, jewelry, and decorative objects. Historically used for making stone tools (arrowheads and scrapers) due to its sharp conchoidal edges.

Geological facts

Chert is so durable that it survived through ancient archaeological sites for thousands of years. It can create sparks when struck against steel, which made it vital for early fire-starting and flintlock firearms.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found in riverbeds, glacial deposits, and as nodules within limestone or shale.