metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Reddish-brown to tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Reddish-brown to tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Reddish-brown to tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture and landscaping.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Found globally in mountain ranges or as water-worn cobbles in riverbeds and beaches; identify by its extreme hardness and grainy texture that won't scratch with a steel knife.
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