metamorphic
Quartzite Pebble (River Rock)
Metamorphic Quartzite (predominantly SiO2)
Hardness: 7 (Mohs scale); Color: White to light tan/beige; Luster: Dull to waxy when unpolished; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures conchoidally); Specific gravity: 2.6 – 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- White to light tan/beige
- Luster
- Dull to waxy when unpolished
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Physical properties
Hardness: 7 (Mohs scale); Color: White to light tan/beige; Luster: Dull to waxy when unpolished; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures conchoidally); Specific gravity: 2.6 – 2.65.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing sand grains to recrystallize into a solid mass. Its rounded shape suggests it was later eroded and smoothed by high-energy water environments like rivers or coastal shorelines.
Uses & applications
Used in construction as a sturdy road base or concrete aggregate, in landscaping for decorative 'river rock' ground cover, and occasionally as an abrasive or in glassmaking if chemical purity is high.
Geological facts
Quartzite is one of the hardest and most chemically resistant rocks on the Earth's surface. Unlike sandstone, which breaks around sand grains, quartzite is so well-fused that it breaks through the grains.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its gritty (yet smooth-to-the-touch) sugary texture when broken. Commonly found in glacial deposits, riverbeds, and mountainous regions where ancient sedimentary basins were uplifted.
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