metamorphic
Quartzite
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale. Color: Off-white to light gray with beige and brownish weathering. Luster: Vitreous to waxy/greasy. Crystal Structure: Trigonal (microcrystalline/interlocked quartz grains). Cleavage: None (conchoidal or irregular fracture). Specific Gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light gray with beige and brownish weathering
- Luster
- Vitreous to waxy/greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: Off-white to light gray with beige and brownish weathering. Luster: Vitreous to waxy/greasy. Crystal Structure: Trigonal (microcrystalline/interlocked quartz grains). Cleavage: None (conchoidal or irregular fracture). Specific Gravity: ~2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone under extreme heat and pressure, causing original quartz sand grains to recrystallize and interlock densely.
Uses & applications
Used extensively as crushed stone for road construction, railway ballast, aggregate in concrete, decorative landscape rock, and historically for stone tools.
Geological facts
Quartzite is so hard and tightly interlocked that when broken, fractures cut directly through the individual quartz grains rather than along the boundaries between them, unlike its parent rock sandstone.
Field identification & locations
Identified by its extreme hardness (scratches glass and steel easily), sugary to fused texture, and lack of reaction to acid. Found abundantly in mountainous regions, ancient metamorphic shields, and eroded river deposits worldwide.
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