metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically grey or white, but often reddish or brown due to iron impurities; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: approx. 2.6
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey or white, but often reddish or brown due to iron impurities; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: approx. 2.6
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. It can be found in mountain belts and areas of ancient crustal movement across all geological eras.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative stone for countertops, tiles, and landscaping; high-purity varieties are used to produce silicon and glass.
Geological facts
Quartzite is so tough that it often outlasts the rocks around it, forming the resistant ridges and peaks of many mountain ranges. It is significantly harder and more durable than the sandstone from which it originated.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (it will easily scratch glass). Unlike marble, it will not fizz with acid. It is commonly found in riverbeds as rounded, smoothed cobbles or in massive outcrops.
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