metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, pink, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (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 (Mohs scale); Color: White, gray, pink, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together, or undergo pressure solution where grains become tightly interlocked.
Uses & applications
Used in construction (crushed stone for road beds), architectural stone for flooring and walls, glass manufacturing (if high purity), and sometimes as a lapidary material for decorative carvings.
Geological facts
Quartzite is so durable that it often forms the caprock or backbone of mountain ranges because it resists weathering much better than surrounding rocks. It creates very thin, acidic soil when it does eventually erode.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and dense, sugary texture. Unlike sandstone, when broken, quartzite breaks through the quartz grains rather than around them. Common in Appalachian and Rocky Mountain ranges.
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