sedimentary

Chert (Flint Pebbles)

Chert (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Gray, bluish-gray, brown, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.6

Hardness: 6

Identified July 14, 2026More sedimentary →

Explore Chert (Flint Pebbles) 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 organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine or groundwater environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools due to its sharp edges when broken. Modern uses include road surfacing, decorative landscaping, and occasionally as a source of silica in gem-cutting for lapidary enthusiasts.

Geological facts

Chert is so durable that it often survives as rounded pebbles in stream beds or on beaches long after the surrounding limestone base rock has eroded away. The dark gray variety is commonly referred to as flint.

Field identification & locations

Identify in the field by its high hardness (it will scratch glass and steel), conchoidal fracture (smooth, curved breaks), and waxy texture. Commonly found in riverbeds, glacial tills, and coastal areas.