sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with iron oxide staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey with iron oxide staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with iron oxide staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or freshwater environments. This specific specimen appears to be a rounded river cobble, suggesting mechanical weathering and transport over a long geological period.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges. Currently used as construction aggregate, road base, and occasionally as decorative landscaping stone.
Geological facts
Chert is so durable that it often survives the weathering of its original host rock. It is one of the most common materials found in riverbeds worldwide. When struck with steel, high-quality chert can produce sparks.
Field identification & locations
Identified in the field by its hardness (cannot be scratched by a steel knife), smooth rounded texture if water-worn, and conchoidal (shell-like) fracture patterns if broken. Common in limestone regions and gravel bars.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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