metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale; Color: typically gray or white; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65
- Hardness
- 7 on Mohs scale
- Color
- typically gray or white
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically gray or white; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65
Formation & geological history
Formed through the heating and pressure of quartz-rich sandstone (metamorphism) in orogenic belts. Most specimens are hundreds of millions of years old.
Uses & applications
Used as railway ballast, in road construction, as decorative stone siding, and occasionally as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, leading it to cap many mountain peaks and ridges across the globe.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that resists crumbling. Commonly found in mountainous regions or as river-smoothed cobbles.
