metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on the Mohs scale, Color: Varies from white and gray to reddish or brown due to iron oxides, Luster: Vitreous to greasy, Crystal structure: Interlocking quartz crystals, Cleavage: None (fractures conchoidally through grains), Specific gravity: 2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: Varies from white and gray to reddish or brown due to iron oxides, Luster: Vitreous to greasy, Crystal structure: Interlocking quartz crystals, Cleavage: None (fractures conchoidally through grains), Specific gravity: 2.65
Formation & geological history
Formed under high heat and pressure from quartz-rich sandstone during tectonic metamorphism, often over hundreds of millions of years in mountain-building environments.
Uses & applications
Used in construction, as crushed stone for road bases, railway ballast, dimension stone, and occasionally for decorative landscaping or sculpture.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich rocks often survive long journeys to end up as smooth pebbles or boulders on beaches.
Field identification & locations
Can be identified in the field by its high hardness (scratches glass easily, cannot be scratched by a knife) and the fact that it breaks across the quartz grains rather than around them like sandstone. Common worldwide in ancient orogenic belts.
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