metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (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 (granular texture); 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, causing the original quartz grains to recrystallize and fuse together.
Uses & applications
Used as crushed stone in road construction, as dimension stone in architecture (countertops, flooring), and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks; it can be differentiated from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and the sugary appearance of fused quartz grains. Commonly found in folded mountain belts worldwide.
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