sedimentary
Banded Chert (with Quartz Vein)
Microcrystalline Silica (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Dark grey to black matrix with white bands; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 6
- Color
- Dark grey to black matrix with white bands
- Luster
- Dull to waxy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Dark grey to black matrix with white bands; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation in marine environments. The white bands are secondary quartz veins formed when silica-rich fluids filled cracks in the host rock over millions of years.
Uses & applications
Used historically for stone tools due to its sharp edges; today used for decorative garden stones, tumbling, and occasionally in jewelry as ornemental stones.
Geological facts
Chert is so hard it can scratch steel and was used by prehistoric humans to start fires when struck against iron or steel, creating sparks.
Field identification & locations
Identify by its extreme hardness and smooth, waxy surface when polished. Commonly found on beaches or in riverbeds where water has rounded the stone. Can be found globally in limestone and chalk formations.
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