metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or light tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, which causes the individual quartz grains to recrystallize and fuse together. It can range from Precambrian to more recent geological ages.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone for flooring and walls. High-purity quartzite is used to produce silica sand for glassmaking and industrial silicon.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of ridges and resistant hilltops because it weathers much more slowly than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through quartz grains rather than around them. Found globally in mountainous regions and areas of ancient shield rock.
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