metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, sometimes reddish or brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to grey, sometimes reddish or brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey, sometimes reddish or brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into a locked mosaic of crystals.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative stone for countertops and tiles; and historically used 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 hills, as it resists weathering and erosion much better than surrounding rocks.
Field identification & locations
Identify in the field by its inability to be scratched by steel, its sugary texture, and the way it breaks through the quartz grains rather than around them. Common in metamorphic belts worldwide.
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