sedimentary

Chert Pebble

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, brown, and reddish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, brown, and reddish-tan
Luster: Dull to waxy

Identified June 27, 2026More sedimentary →

Explore Chert Pebble in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Gray, brown, and reddish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary rock layers like limestone. This specific specimen has been water-worn and rounded in a high-energy environment like a river or beach.

Uses & applications

Historically used for stone tools and starting fires (flint). Currently used as decorative gravel, in jewelry (when polished), and for road construction ballast.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has eroded away. The reddish hues in this specimen are likely caused by iron oxide (limonite or hematite) impurities.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth waxy texture when broken, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and glacial tills globally.