sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, earthy tones; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Brown, tan, earthy tones
Luster: Dull to waxy

Identified July 14, 2026More sedimentary →

Explore Chert (River 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: 6.5-7 Mohs; Color: Brown, tan, earthy tones; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in sedimentary environments. These pebbles are typically worn smooth by water transport in rivers.

Uses & applications

Historically used for stone tools/fire-starting; currently used for landscaping, aggregate in construction, and as aquarium or decorative stones.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles in riverbeds long after other rocks have eroded away. It was a primary material for prehistoric arrowheads.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, rounded 'water-worn' texture. Found globally in riverbanks, beaches, and gravel pits.