metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Grayish-white to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-white to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-white to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); 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 from tectonic activity, the original quartz grains recrystallize and fuse together, creating a hard, durable rock.
Uses & applications
Used extensively in road construction (as crushed stone), as railway ballast, for flooring and wall coverings, and historically for making stone tools due to its hardness.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists erosion better than the surrounding softer rocks. It will scratch glass easily.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will scratch steel and glass). Unlike limestone, it will not fizz when exposed to acid. Found globally in ancient mountain belts and shield areas.
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