metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or reddish due to iron oxides; Luster: Vitreous or dull; Structure: Granofelsic, interlocking quartz grains; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or reddish due to iron oxides
- Luster
- Vitreous or dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or reddish due to iron oxides; Luster: Vitreous or dull; Structure: Granofelsic, interlocking quartz grains; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone under intense heat and pressure, causing the original quartz grains to recrystallize into a dense, hard stone.
Uses & applications
Used as crushed stone for road construction, railroad ballast, decorative landscaping, and occasionally as high-end building stone or countertops.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is more resistant to weathering than the sandstone from which it originated, often forming prominent mountain ridges.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it breaks across the quartz grains rather than around them). Commonly found in ancient mountain belts and riverbeds as rounded cobbles.
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