metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible reddish stains from iron; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or tan with possible reddish stains from iron
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible reddish stains from iron; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. It can be found in mountain belts globally, ranging from Precambrian to more recent geological ages.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping or interior design. High-purity quartzite is a source of silica for glass and silicon metal production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists erosion better than the surrounding rocks.
Field identification & locations
In the field, it is identified by its extreme hardness (cannot be scratched by steel) and the way it breaks through the quartz grains rather than around them, unlike sandstone. Common in glacial till and riverbeds.
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