sedimentary
Chert (Iron-Stained)
Silicon Dioxide (SiO2) with Ferric Oxide (Fe2O3) impurities
Hardness: 7 on Mohs scale; Color: Grey core with yellow, orange, and brown rust-like staining; Luster: Dull to waxy; Structure: Microcrystalline; Fracture: Conchoidal (shell-like curves); Opaque.
- Hardness
- 7 on Mohs scale
- Color
- Grey core with yellow, orange, and brown rust-like staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey core with yellow, orange, and brown rust-like staining; Luster: Dull to waxy; Structure: Microcrystalline; Fracture: Conchoidal (shell-like curves); Opaque.
Formation & geological history
Chemically precipitated from silica-rich fluids in marine environments or formed through the replacement of limestone. The yellow/orange staining is due to iron oxidation (limonite/hematite) from weathering over geological time.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for landscaping, road construction, and occasionally as an ornamental lapidary material.
Geological facts
Chert is so durable that it often survives as stream gravel long after the surrounding softer rocks have eroded away. It was a primary material for prehistoric flintknapping.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved conchoidal fracture. Commonly found in riverbeds, glacial tills, and as nodules in limestone outcrops.
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