sedimentary
Chert (River Pebble)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with reddish iron staining; Luster: Dull to waxy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with reddish iron staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with reddish iron staining; Luster: Dull to waxy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specific specimen shows rounding and smoothing from fluvial (river) transport and erosion.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for high-friction road construction, landscaping, and as a source of silica.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads, scrapers, and fire-starting tools because it breaks with a predictable, razor-sharp edge.
Field identification & locations
Identify by its extreme hardness (scratches glass), smooth texture, and curved, shell-like fracture marks. Frequently found in riverbeds, glacial tills, and limestone outcrops.
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