metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to light gray; Luster: Dull/Waxy (tumbled); Structure: Recrystallized interlocking quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light gray
- Luster
- Dull/Waxy (tumbled)
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white to light gray; Luster: Dull/Waxy (tumbled); Structure: Recrystallized interlocking quartz grains; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Often found as water-worn pebbles in riverbeds or glacial deposits.
Uses & applications
Used in construction as crushed stone, as a refractory material in metallurgy, and in landscaping. Highly polished versions are used for decorative purposes.
Geological facts
Quartzite is so hard that when it breaks, it breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock sandstone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in areas with metamorphic terrane or glacial outwash plains.
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