sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
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 More sedimentary →
Explore Chert (River Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
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.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary