metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous or sugary; Crystal structure: hexagonal (cryptocrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white to light gray
- Luster
- vitreous or sugary
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous or sugary; Crystal structure: hexagonal (cryptocrystalline); 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, typically in convergent plate boundaries. The original quartz sand grains recrystallize into a locked mosaic of quartz crystals.
Uses & applications
Used in construction as crushed stone or road ballast, as decorative stone in architecture, and occasionally in glassmaking if the purity is high enough. It was historically used for making stone tools due to its hardness.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists weathering much better than the rocks around it.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its sugary, granular appearance that looks like sandpaper but feels smooth to the touch. It is found worldwide in metamorphic belts.
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