metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Light gray, tan, or white; Luster: Vitreous to greasy; Crystal structure: Trigonal (microcrystalline/interlocking quartz grains); Cleavage: None (fractures conchoidally); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Light gray, tan, or white
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale; Color: Light gray, tan, or white; Luster: Vitreous to greasy; Crystal structure: Trigonal (microcrystalline/interlocking quartz grains); Cleavage: None (fractures conchoidally); Specific Gravity: 2.65
Formation & geological history
Formed from quartz-rich sandstone subjected to high heat and pressure during regional or contact metamorphism, typically occurring in mountain-building belts over millions of years.
Uses & applications
Used in construction, railroad ballast, decorative landscaping, manufacturing of silica bricks, and occasionally tumbled or carved for ornamental purposes.
Geological facts
Quartzite is extremely resistant to weathering and erosion, which is why quartz-rich rocks often survive as rounded pebbles in rivers and beaches long after other minerals have weathered away.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily and cannot be scratched by a knife), lack of reaction to acid, and a sugary texture on broken surfaces where quartz grains fracture through rather than around.
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