metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, tan; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 7 on Mohs scale
- Color
- White, gray, tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, tan; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together into a dense, interlocking matrix.
Uses & applications
Used in construction as road ballast, railway ballast, and decorative stone. High-purity quartzite is crushed to produce silica sand for glassmaking and metallurgy.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the resistive ridges and peaks in mountain ranges. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify by its sugary texture and extreme hardness. Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain belts globally.
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