metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown (from iron oxidation); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and reddish-brown (from iron oxidation)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown (from iron oxidation); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction as crushed stone for road beds and railway ballast, as decorative building stone, and historically as a tool stone for making projectile points and scrapers.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. It is often confused with marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify it by its extreme hardness (it will easily scratch glass) and its granular, sugary texture. It is found in mountain ranges globally and metamorphic belts.
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