sedimentary

Fossiliferous Chert

Cryptocrystalline quartz (SiO2) with biogenic inclusions

AI-generated identification · may be incorrect

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 July 19, 2026More sedimentary →

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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.