metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or yellow/tan (due to iron oxidation); Luster: Vitreous to dull; Crystal structure: Hexagonal (as quartz grains); Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or yellow/tan (due to iron oxidation)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or yellow/tan (due to iron oxidation); Luster: Vitreous to dull; Crystal structure: Hexagonal (as quartz grains); Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, hard rock structure.
Uses & applications
Used extensively in construction for road ballast, floor tiles, roofing, and as decorative stone/countertops. High-purity quartzite is also used to produce silica for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is much more durable than the sandstone it originates from and often forms the literal backbone of mountain ranges because it is highly resistant to chemical and physical weathering.
Field identification & locations
Identify in the field by its extreme hardness and the way it fractures through grains rather than around them (unlike sandstone). It is commonly found in folded mountain belts globally, such as the Appalachians or the Alps.
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