sedimentary
Fossiliferous Chert
Cryptocrystalline quartz (SiO2) with biogenic inclusions
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Specific gravity: approx. 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or yellowish-brown
- Luster
- Waxy to dull
Identified More sedimentary →
Explore Fossiliferous Chert in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Specific gravity: approx. 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. It often traps microfossils or larger organisms like crinoids or shells during diagenesis.
Uses & applications
Historically used for stone tools (knapping) due to its sharp fracture edges. Today it is used in road aggregate, as decorative gravel, and for lapidary items like beads.
Geological facts
This specimen shows circular inclusions that likely represent cross-sections of crinoid stem ossicles or small shell fragments. Chert is extremely durable and often survives weathering better than its surrounding host rock.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture surfaces. Often found in riverbeds or as nodules in limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Shale
Argillaceous sedimentary rock
sedimentary