sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically tan, grey, brown, or white with dark banding; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically tan, grey, brown, or white with dark banding
Luster: waxy to dull

Identified March 18, 2026More sedimentary →

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 organic remains (like radiolarians or diatoms) or chemical precipitation from sea water. This specimen appears as a water-worn river or beach pebble, shaped by erosion over millions of years.

Uses & applications

Historically used for stone tools and weapons due to its sharp conchoidal fracture. Modern uses include decorative gravel, landscaping, and lapidary work (polished stones).

Geological facts

Chert is so durable that it often survives long after the surrounding softer limestone or chalk has eroded away. It was one of the most vital materials for prehistoric humans for crafting scrapers and arrowheads.

Field identification & locations

Identified in the field by its superior hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture pattern. Commonly found in riverbeds, glacial till, and coastal areas.