sedimentary
Chert (containing Fossil Mold)
Silicon dioxide (SiO2)
Hardness: 6.5-7 Mohs scale; Color: Cream, tan, grey; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 6
- Color
- Cream, tan, grey
- 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: Cream, tan, grey; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments, often replacing original limestone. These can date from the Precambrian to recent eras.
Uses & applications
Historically used for stone tools/arrowheads. Modern uses include abrasives, road construction, and as aquarium or landscape decor.
Geological facts
Chert is so hard it can spark when struck against steel. The indentation in this specimen appears to be a fossil mold where a shell or organic matter was once embedded before dissolving.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel pocketknife) and its smooth, shell-like fracture surfaces. Frequently found in limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary