metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific Gravity: 2.6-2.7. It is extremely tough and breaks through quartz grains rather than around them.
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific Gravity: 2.6-2.7. It is extremely tough and breaks through quartz grains rather than around them.
Formation & geological history
Quartzite is a non-foliated metamorphic rock that forms when quartz-rich sandstone is subjected to high heat and pressure, typically during tectonic plate collisions. This process causes the original quartz sand grains to recrystallize into an interlocking mosaic.
Uses & applications
Used extensively in road construction and railroad ballast because of its hardness. High-purity quartzite is used in glass making and electronics. Crushed quartzite is used as a soil conditioner and in abrasive manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains, resisting weather better than surrounding rock types. It can sometimes be mistaken for marble, but can be distinguished by its inability to be scratched by a steel knife.
Field identification & locations
Identify in the field by its sugary texture on fresh surfaces and its ability to scratch glass. It will not fizz when exposed to acid (unlike marble). Commonly found in ancient mountain belts and shield areas worldwide.
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