sedimentary
Chert (Smooth River Pebble)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, grey, or tan (due to iron impurities); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8.
- Hardness
- 6
- Color
- Brown, grey, or tan (due to iron impurities)
- 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 on Mohs scale; Color: Brown, grey, or tan (due to iron impurities); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments; geological age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as river rock for landscaping.
Geological facts
Chert is so hard it can scratch glass. When struck against steel, it produces sparks, which led to its historical use in flintlock firearms and primitive fire-starting kits.
Field identification & locations
Identify by its 'waxy' appearance and smooth, rounded edges if found in water; it often displays a curved (conchoidal) fracture when broken. Found globally in riverbeds and sedimentary basins.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary