metamorphic
Quartzite Pebble
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: Light gray to tan; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Light gray to tan
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Light gray to tan; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, typically in orogenic belts. This specific specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Used as decorative gravel in landscaping, as an abrasive, and in construction as a sturdy aggregate. Highly pure quartzite is a source of silica for glass making.
Geological facts
Quartzite is so durable that it often outlasts the mountains it was formed in, becoming the primary component of river gravels and beach pebbles. It is one of the hardest common rocks found on Earth's surface.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in riverbeds, glacial tills, and beaches. Collectors value well-rounded, smooth shapes.
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