metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (harder than glass). Color: Pink, reddish-brown, or grey. Luster: Vitreous to dull. Structure: Non-foliated, granular. Cleavage: None; fractures through quartz grains rather than around them.
- Hardness
- 7 on Mohs scale (harder than glass)
- Color
- Pink, reddish-brown, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass). Color: Pink, reddish-brown, or grey. Luster: Vitreous to dull. Structure: Non-foliated, granular. Cleavage: None; fractures through quartz grains rather than around them.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Often found in Precambrian or Paleozoic mountain belts.
Uses & applications
Used in construction as road ballast, railway tracks, and building stone. Crushed quartzite is used in the manufacture of glass and ceramics. High-purity quartzite is a source of silica for silicon production.
Geological facts
Quartzite is so tough that it often forms the resistive cap rock on ridges or mountain summits. It is often confused with marble but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify in the field by its sugary texture and the way it breaks through sand grains. It does not fizz with acid. Common in the Appalachian Mountains, parts of Brazil, and the Lake Superior region.
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