metamorphic
Quartzite
Quartzite (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with yellow-brown iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with yellow-brown iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with yellow-brown iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture)
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for flooring and walls. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of ridges and mountains. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify by its sugary, granular texture and extreme hardness. Unlike marble, it will not fizz when exposed to acid. Found globally in metamorphic belts like the Appalachian Mountains or the Scottish Highlands.
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