metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or red from impurities; Luster: vitreous to dull; Crystal structure: Trigonal; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or red from impurities; Luster: vitreous to dull; Crystal structure: Trigonal; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together.
Uses & applications
Used as crushed stone in construction, railway ballast, and decorative stone. High-purity quartzite is used in glass making and chemical industries.
Geological facts
Quartzite is so hard and durable that it often forms the tops of hills and ridges because it resists erosion much better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and the fact that it breaks through the sand grains rather than around them. Common in mountain belts like the Appalachians or Alps.
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