metamorphic
Quartzite
Quartzite (Metamorphosed Quartz Sandstone)
Hardness: 7 on the Mohs scale; Color: typically white to gray, but can be pink, red, or yellow due to impurities; Luster: vitreous to greasy; Crystal structure: interlocking quartz grains; Cleavage: none (fractures conchoidally through grains, not around them); Specific gravity: 2.65 - 2.75.
- Hardness
- 7 on the Mohs scale
- Luster
- vitreous to greasy
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Physical properties
Hardness: 7 on the Mohs scale; Color: typically white to gray, but can be pink, red, or yellow due to impurities; Luster: vitreous to greasy; Crystal structure: interlocking quartz grains; Cleavage: none (fractures conchoidally through grains, not around them); Specific gravity: 2.65 - 2.75.
Formation & geological history
Formed under high heat and pressure conditions when quartz-rich sandstone is subjected to regional or contact metamorphism. The original quartz grains recrystallize along with the cementing material, forming an interlocked mosaic of quartz crystals.
Uses & applications
Used in construction, as crushed stone for road building, as a decorative dimension stone, for railway ballast, and in the manufacturing of silica brick and ferroalloys.
Geological facts
Because quartzite is extremely hard and resistant to chemical weathering, ridges underlain by quartzite often form prominent hills or mountain ridges in the landscape.
Field identification & locations
Can be identified in the field by its sugary texture on fractured surfaces and its inability to be scratched by a steel knife, alongside the fact that it breaks across quartz grains rather than around them.
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