metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.63-2.65
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.63-2.65
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing the individual quartz grains to recrystallize into a dense network of interlocking crystals.
Uses & applications
Used as crushed stone for road construction, railroad ballast, decorative building stone, and occasionally in the glass industry if purity is high.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion better than surrounding rocks, frequently forming the tops of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the fact that fractures will break through the quartz grains rather than around them, unlike sandstone. Found globally in ancient mountain belts.
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