metamorphic
Quartzite
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish due to iron; Luster: vitreous to waxy; Texture: granular, crystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan but can be reddish due to iron
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish due to iron; Luster: vitreous to waxy; Texture: granular, crystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating an extremely durable rock.
Uses & applications
Used in construction as road ballast, roofing granules, and dimension stone for flooring or countertops. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it weathers much more slowly than surrounding rocks.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and its sugary, crystalline surface that breaks across the grains rather than around them. Common in folded mountain belts and ancient shield regions.
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