sedimentary

Chert (Yellow Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Tan, yellow, or mustard brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Tan, yellow, or mustard brown
Luster: Waxy to dull

Identified June 19, 2026More sedimentary →

Explore Chert (Yellow Jasper) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Tan, yellow, or mustard brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed by the precipitation of silica from groundwater in sedimentary environments or as biochemical deposits on the ocean floor. Most specimens found in surface gravels date from various Phanerozoic periods.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include landscaping, as a lapidary material for tumbling, and in jewelry as yellow jasper.

Geological facts

Chert is so hard it can create sparks when struck against steel. It was one of the most important materials for early human technology due to its sharp conchoidal edges.

Field identification & locations

Identified by its smooth, waxy surface and curved, glass-like fracture patterns. Commonly found in riverbeds, glacial tills, and as nodules within limestone or chalk.