metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white/light tan; Luster: vitreous to waxy; Crystal structure: Hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6 – 2.7
- Hardness
- 7 on Mohs scale
- Color
- white/light tan
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: white/light tan; Luster: vitreous to waxy; Crystal structure: Hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6 – 2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure. This process causes the individual quartz grains to recrystallize and fuse into a dense, solid rock lattice.
Uses & applications
Used in construction as road ballast, flooring, and wall facing. Sometimes used defensively as stone tools in history. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent sandstone.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and its sugary/crystalline texture on fresh surfaces. Often found in mountainous regions or ancient coastal deposits.
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