sedimentary

Polished chert (likely jasper or iron-rich chert)

Microcrystalline quartz, SiO₂, colored by iron oxides and possibly clay minerals

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; mustard-yellow to brown with darker gray-brown patches, waxy to glassy luster, very fine-grained cryptocrystalline structure, and no visible cleavage. The rounded, glossy surface indicates tumbling or natural water wear.

Identified September 6, 2026More sedimentary →

Explore Polished chert (likely jasper or iron-rich chert) 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

Chert forms when silica-rich groundwater replaces or precipitates within sediment, commonly in limestone or marine deposits; iron oxidation produces the yellow-brown coloration. Its exact geological age cannot be determined from the image, but chert ranges from Precambrian to recent formations.

Uses & applications

Used for ornamental stone, cabochons, carvings, and lapidary pieces; historically, chert was knapped for sharp tools and weapons. It is not usually a major construction stone in small specimens.

Geological facts

A steel file or quartz crystal should scratch it, while a fingernail will not. Conchoidal fracture and a waxy appearance are characteristic of chert; stronger red, orange, or patterned material may be marketed as jasper.

Field identification & locations

Common in sedimentary terrains worldwide, including the United States, Mexico, Europe, and Australia. The exact variety is uncertain without a fresh fracture, hardness test, and locality information.