metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, pink, or reddish-brown; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, pink, or reddish-brown
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, pink, or reddish-brown; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.7.
Formation & geological history
Formed from the recrystallization of quartz-rich sandstone through intense heat and pressure (metamorphism). Usually associated with convergent plate boundaries and mountain-building events.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in countertops and floor tiles. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them, unlike its parent rock, sandstone. It is extremely resistant to chemical weathering.
Field identification & locations
Identify in the field by its grainy, sandpaper-like texture that lacks the distinct layering of shale. It will scratch glass easily. Commonly found in folded mountain ranges across the globe, such as the Appalachians or the Alps.
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