sedimentary
Chert (River Pebble)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs. Color: Dull grey, olive-green, or brownish. Luster: Waxy to dull. Structure: Microcrystalline with conchoidal fracture. Cleavage: None. Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Dull grey, olive-green, or brownish
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 Mohs. Color: Dull grey, olive-green, or brownish. Luster: Waxy to dull. Structure: Microcrystalline with conchoidal fracture. Cleavage: None. Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen has been rounded and smoothed by water erosion in a stream or river bed.
Uses & applications
Historically used for arrowheads and scrapers due to its sharp edges when broken. Today used as decorative gravel, in road construction, and as aquarium stones.
Geological facts
Chert is a very hard and durable rock that can survive long periods of transport in rivers. It is essentially the same material as flint, but the term flint is usually reserved for nodules found in chalk or limestone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy feel. Often found in riverbeds, gravel pits, and sedimentary outcrops globally.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary