metamorphic
River Cobble (likely Quartzite)
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to greyish-beige; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None; Specific Gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan to greyish-beige
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to greyish-beige; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None; Specific Gravity: 2.6-2.65
Formation & geological history
Formed from quartz-rich sandstone subjected to intense heat and pressure (metamorphism). Usually smoothed into a rounded shape by hydraulic erosion in riverbeds or coastal environments.
Uses & applications
Commonly used as decorative landscaping stones, road aggregate, and sometimes as a component in glass manufacturing if high purity.
Geological facts
Quartzite is one of the most durable and resistant rocks on Earth's surface, which is why it often survives long-distance transport in rivers while other stones wear away.
Field identification & locations
Identify by its ability to scratch glass and its smooth, water-worn texture. Commonly found in riverbeds, glacial deposits, and along beaches.
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