metamorphic
Quartzite
Quartzite (SiO2 composition)
Hardness: 7 on the Mohs scale. Color: Light grey to off-white, light beige. Luster: Vitreous to dull/sugary. Crystal Structure: Trigonal (microcrystalline quartz grains). Cleavage: None (conchoidal to irregular fracture). Specific Gravity: ~2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Light grey to off-white, light beige
- Luster
- Vitreous to dull/sugary
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Physical properties
Hardness: 7 on the Mohs scale. Color: Light grey to off-white, light beige. Luster: Vitreous to dull/sugary. Crystal Structure: Trigonal (microcrystalline quartz grains). Cleavage: None (conchoidal to 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 the individual quartz grains to recrystallize and interlock tightly.
Uses & applications
Widely used as crushed stone in road construction, railway ballast, building stone, decorative landscaping gravel, and historically as a raw material for stone tools.
Geological facts
Unlike sandstone, which breaks around its sand grains, quartzite breaks directly through the recrystallized quartz grains due to its immense density and interlocking crystalline matrix.
Field identification & locations
Identify in the field by its sugary texture, extreme hardness (scratches glass easily), and rounded river-pebble morphology. Very common in riverbeds, glacial deposits, and mountainous metamorphic terranes worldwide.
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