metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in convergent plate boundaries or orogenic belts.
Uses & applications
Used in construction for road ballast, flooring, wall coverings, and countertops. High-purity quartzite is used to produce silica for glass and silicon metal.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in mountainous regions or as rounded pebbles in riverbeds.
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