metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, typically during mountain-building events (orogeny).
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop material. Also used as a decorative stone in landscaping and architecture due to its durability.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the capstones of hills and ridges, as it resists erosion much better than the surrounding rock types. It will scratch glass easily.
Field identification & locations
Identify in the field by its sugary, granular texture and extreme hardness (it cannot be scratched by a steel knife). Common in tectonic belts and ancient shield areas. Collectors look for pieces with unique inclusions or colors.
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