metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White, gray, pink, or reddish-brown due to iron impurities. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.6–2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, pink, or reddish-brown due to iron impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White, gray, pink, or reddish-brown due to iron impurities. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.6–2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism). This process causes the original quartz grains to recrystallize and fuse together into a dense, hard rock. It can be found in mountain belts globally.
Uses & applications
Used in construction as crushed stone for road beds, as railway ballast, and as a dimension stone for flooring, walls, and countertops. It is also used as a source of silica for glass manufacturing.
Geological facts
Quartzite is so hard and durable that it often remains as ridges or peaks on mountains after softer surrounding rocks have eroded away. It is often confused with marble, but can be distinguished by its ability to scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (scratches steel) and its grainy, sandpaper-like texture that has been fused into a crystalline mass. It is commonly found in river beds as rounded cobbles or in massive mountain outcrops.
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