sedimentary
Chert (Nodule)
Silicon Dioxide (SiO2)
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
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Physical properties
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.
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.
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