River Cobble (likely Quartzite)

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.

Identified on: 5/1/2026

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