metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (scratches glass). Color: White, gray, or pale pink. Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal (but appears as interlocking grains). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- White, gray, or pale pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass). Color: White, gray, or pale pink. Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal (but appears as interlocking grains). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together, creating an extremely hard, dense rock. It can range in geological age from Precambrian to more recent orogenic periods.
Uses & applications
Used heavily in construction as crushed stone for road ballast, railroad ballast, and concrete aggregate. High-purity quartzite is used to produce glass and silicon metal. It is also popular as decorative stone, countertops, and floor tiles due to its extreme durability.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. Some types of quartzite, like 'Taj Mahal' quartzite, are highly prized in luxury interior design for having the look of marble with the strength of granite.
Field identification & locations
Identify in the field by its hardness (it should easily scratch a steel knife or glass) and its sugary, crystalline texture that breaks through the grains rather than around them. It is commonly found in fold mountain belts worldwide, such as the Appalachians or the Alps. For collectors, look for unique colors caused by metallic impurities.
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