metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan or off-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan or off-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan or off-white; Luster: Vitreous to dull; 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. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can be found in mountain ranges and orogenic belts worldwide.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in countertops and floor tiles. High-purity quartzite is used to produce ferrosilicon and silicon metal.
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 rock, sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sugary texture. It is often found in ridgelines because it is highly resistant to weathering.
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