metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); 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/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogenic processes). The sand grains recrystallize into an interlocking mosaic of quartz crystals.
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. Highly crushed quartzite is used in glass making and as an industrial abrasive. Polished specimens are used for decorative architecture and countertops.
Geological facts
Quartzite is extremely resistant to chemical weathering and erosion, which is why it often forms the peaks and ridges of mountain ranges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its sugary, granular texture when fractured. Unlike marble, it will not fizz with acid. Common in ancient mountain belts globally.
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