metamorphic
River Rock (likely Quartzite or Quartz-rich Siltstone)
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Light tan to grayish-white, Luster: Dull to waxy when unpolished, Crystal Structure: Granoblastic (fine-grained), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Light tan to grayish-white, Luster: Dull to waxy when unpolished, Crystal Structure: Granoblastic (fine-grained), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under heat and pressure. This specific specimen has been rounded and smoothed by fluvial transport (moving water) over thousands of years.
Uses & applications
Commonly used as decorative landscaping stone, in construction aggregates, or as tumbled stones for aquarium and craft use.
Geological facts
Quartzite is so hard that it can scratch glass and steel. Most river stones like this have traveled hundreds of miles, losing their sharp edges through mechanical weathering against other rocks in streambeds.
Field identification & locations
Identify in the field by its rounded shape, smoothness, and extreme hardness (it will not be easily scratched by a pocket knife). Found globally in riverbeds, glacial deposits, and beaches.
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