sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, beige, or grey with possible banding; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, beige, or grey with possible banding
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from aqueous fluids or the replacement of limestone/dolomite. Often found in marine sedimentary layers as nodules or beds, dating back to various geological eras from the Precambrian to present.

Uses & applications

Historically used for stone tools (flintknapping); currently used in road construction as aggregate, in ceramics, and as decorative landscape stones.

Geological facts

Chert is so hard it can scratch steel and was used for centuries to create sparks for starting fires and for early firearms. It often contains microfossils of radiolarians or sponges.

Field identification & locations

Identify in the field by its smooth, waxy feel, conchoidal (shell-like) fractures, and its inability to be scratched by a steel knife. Commonly found in riverbeds or limestone outcrops.