metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with some iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with some iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with some iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization of quartz grains into a dense, interlocking mosaic.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for flooring or countertops. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains. It is harder than glass and cannot be scratched by a steel knife.
Field identification & locations
Identified in the field by its extreme hardness and the fact that it breaks across the quartz grains rather than around them. Found globally in ancient mountain belts and cratons.
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