metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or grayish-tan with occasional inclusions; Luster: Vitreous to greasy; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or grayish-tan with occasional inclusions
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or grayish-tan with occasional inclusions; Luster: Vitreous to greasy; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Quartzite is formed through the metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, typically in orogenic (mountain-building) belts. Most specimens range from Proterozoic to Phanerozoic in age.
Uses & applications
Used in construction for road ballast, roofing granules, and as a dimension stone for flooring or wall cladding. Pure varieties are used to produce silica sand for glassmaking and industrial abrasives. High-quality pieces are used in decorative landscaping and lapidary work.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming prominent ridges and peaks in mountain ranges. It is often confused with marble, but unlike marble, it will not fizz when exposed to acid and is hard enough to scratch glass.
Field identification & locations
Identify in the field by its sugary texture on fresh breaks and its extreme hardness (cannot be scratched by a steel knife). It is commonly found in ancient mountain roots and glacial deposits. For collectors, look for versions with interesting mineral inclusions or coloring.
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