metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, or brownish-gray; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, or brownish-gray
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, or brownish-gray; Luster: Dull to vitreous; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together, obliterating the original sedimentary texture.
Uses & applications
Crushed stone for road construction, railway ballast, and as a decorative landscaping stone. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so hard and durable that it often forms the ridges and peaks of mountain ranges because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture that breaks through the grains rather than around them. Commonly found in riverbeds as rounded cobbles.
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