metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or pinkish/tan due to iron oxide; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or pinkish/tan due to iron oxide
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or pinkish/tan due to iron oxide; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. This process causes the quartz grains to recrystallize and fuse together, creating an extremely durable rock.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used in the manufacture of glass and silicon. Polished slabs are used for kitchen countertops and decorative flooring.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is often confused with marble, but unlike marble, quartzite will not fizz in contact with weak acid.
Field identification & locations
Look for a granular, sandpaper-like texture that resists being scratched by a knife. It breaks across grains rather than around them. Commonly found in mountainous regions where tectonic activity has occurred.
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