sedimentary
River Stone (Chert/Siltstone)
Cryptocrystalline Quartz (SiO2) with trace impurities
Hardness: 6.5–7 on Mohs scale; Color: Mottled gray, brown, and black; Luster: Dull to waxy; Structure: Microcrystalline with no visible grains; Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Mottled gray, brown, and black
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Mottled gray, brown, and black; Luster: Dull to waxy; Structure: Microcrystalline with no visible grains; 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 specimen has been significantly smoothed and rounded by long-term fluvial (river) erosion.
Uses & applications
Commonly used as decorative landscaping rock, aquarium substrate, and in construction as aggregate. Historically used for tool-making (flint knapping) due to its conchoidal fracture.
Geological facts
Many river stones like this one have been transported hundreds of miles from their original source by glacial movement or ancient river systems, essentially acting as geological 'time travelers'.
Field identification & locations
Identify in the field by its rounded, water-worn shape and the fact that it cannot be scratched by a steel knife (if chert-heavy). Found globally in riverbeds, glacial till, and beach deposits.
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