metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; 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 sand grains to recrystallize and fuse together, creating an extremely durable rock.
Uses & applications
Used in construction as crushed stone for road gravel and rail ballast, as dimension stone for counter tops and flooring, and occasionally as a source of silica for glass making.
Geological facts
Quartzite is so hard and dense that when it is broken, it fractures through the individual sand grains rather than around them, which is a key distinguishing feature from its parent sandstone.
Field identification & locations
Identify it in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture. It is commonly found in folded mountain belts globally.
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