metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, orange-white; Luster: Vitreous to waxy; Structure: Non-foliated, interlocking quartz crystals; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, orange-white
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, orange-white; Luster: Vitreous to waxy; Structure: Non-foliated, interlocking quartz crystals; 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, original quartz grains recrystallize and fuse together. Can date from various geological periods where tectonic activity occurred.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. Polished pieces are used in decorative architecture and landscaping.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, frequently forming the crests of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and grainy texture that resembles sandpaper but feels smooth to the touch. Look for the way it breaks through the quartz grains rather than around them. Common in mountain ranges and glacial till.
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