sedimentary
Chert (White Chert)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to beige; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Off-white to beige
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Off-white to beige; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Abrasives, construction aggregate, and historically used for stone tools/weaponry due to its sharp edges; used today as landscaping stones or for lapidary tumbling.
Geological facts
Chert is so hard it can create sparks when struck against steel. This specific specimen shows signs of water erosion and possible thermal fracturing or 'crazing' on the surface.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fractures. Often found in gravel beds or eroding out of limestone cliffs.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary