sedimentary
Weathered River Rock (likely Chert or Basalt with algae)
Silicon dioxide (SiO2) with organic biofilm
Hardness: 6.5-7 (Mohs scale), Color: Dull green and brownish-yellow due to algae/silt coating, Luster: Dull/waxy, Structure: Cryptocrystalline, Shape: Sub-angular to rounded water-worn cobble
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Dull green and brownish-yellow due to algae/silt coating, Luster: Dull/waxy, Structure: Cryptocrystalline, Shape: Sub-angular to rounded water-worn cobble
Formation & geological history
Formed through the deposition of silica in marine environments or volcanic activity, then rounded and weathered in a stream or river bed over thousands of years.
Uses & applications
Primarily used in landscaping, construction aggregate, or as aquarium decor; can be used for flint knapping if composed of high-quality chert.
Geological facts
The green color is not intrinsic to the rock but is a layer of river algae (periphyton) and silt. River rocks are often used as tools for grinding by ancient civilizations.
Field identification & locations
Look for smooth, rounded edges and a non-reactive surface to acids. Commonly found in current or ancient riverbeds and glacial deposits. To see the true mineral, one would need to crack it open.
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