metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-green; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); SG: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Grayish-green
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-green; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); SG: 2.65
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating a dense, hard rock.
Uses & applications
Used primarily in construction as crushed stone for road gravel and railroad ballast, in dimensional stone for flooring and countertops, and occasionally for high-silica industrial applications.
Geological facts
Quartzite is so hard and durable that it often remains as ridges or peaks while softer surrounding rocks erode away. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its sugary texture and extreme hardness (cannot be scratched by a steel pocket knife). It breaks across the grains rather than around them. Common in mountainous regions globally.
