metamorphic
Quartzite
Quartzite (Primary mineral: Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (the specimen shown appears tan due to iron staining); Luster: vitreous to waxy; Crystal structure: Trigonal (granular microstructure); Cleavage: None; Specific gravity: 2.6–2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (the specimen shown appears tan due to iron staining); Luster: vitreous to waxy; Crystal structure: Trigonal (granular microstructure); Cleavage: None; Specific gravity: 2.6–2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. While found in many ages, significant deposits often date back to the Proterozoic or Paleozoic eras.
Uses & applications
Used extensively in construction as road ballast, gravel, and railway ballast. Due to its durability and hardness, it is also used for building facades, floor tiles, and as a decorative stone in landscaping.
Geological facts
Quartzite is so durable that it can outlast the surrounding softer rocks in a landscape, often forming prominent ridges or hilltops. Its name comes from its nearly pure quartz content, which makes it resistant to chemical weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its grainy, sugary appearance on a fresh break. Unlike sandstone, quartzite breaks across the individual quartz grains rather than around them. It is commonly found in mountain belts and shield areas globally.
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