sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dark grey/brown with tan banding; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
- Hardness
- 7 Mohs scale
- Color
- Dark grey/brown with tan banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs scale; Color: Dark grey/brown with tan banding; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specimen has been rounded and smoothed by fluvial (river) erosion over thousands of years.
Uses & applications
Historically used for stone tools and fire-starting. Currently utilized in construction aggregate, landscaping, and as decorative river stones.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. It was a primary material for prehistoric arrowheads due to its sharp conchoidal fracturing.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth texture, and characteristic waxy luster when broken. Frequently found in riverbeds, glacial tills, and limestone deposits worldwide.
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