metamorphic
River Rock (Quartzite)
Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: Off-white, tan, or grey. Luster: Dull to vitreous. Structure: Granular, non-foliated. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on the Mohs scale
- Color
- Off-white, tan, or grey
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on the Mohs scale. Color: Off-white, tan, or grey. Luster: Dull to vitreous. Structure: Granular, non-foliated. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from quartz-rich sandstone subjected to high heat and pressure (metamorphism). High-energy fluvial environments (rivers/streams) have since smoothed and rounded the specimen over thousands of years.
Uses & applications
Used in landscaping, construction aggregate, railroad ballast, and occasionally as a base for decorative pebble art or stone engraving.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, leading to the formation of ridges and hilltops. It is chemically stable and resistant to weathering.
Field identification & locations
Identify by its hardness (it will scratch glass) and its smooth, rounded 'water-worn' texture. Found globally in riverbeds, glacial deposits, and beaches. Collectors value it for tumbling or as a 'worry stone'.
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