metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; 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
- Gray, white, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing quartz grains to recrystallize into a locked mosaic.
Uses & applications
Used in construction for road ballast, roofing tiles, flooring, and decorative wall coverings. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the rocks around it, forming prominent ridges and hills. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and the way it breaks through the quartz grains rather than around them (unlike sandstone). Found in mountain ranges globally.
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