metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (pink/brown due to iron impurities); Luster: vitreous to dull; Crystal Structure: Trigonal (granular texture); Cleavage: missing (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, gray, or tan (pink/brown due to iron impurities); Luster: vitreous to dull; Crystal Structure: Trigonal (granular texture); Cleavage: missing (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. Can range from Precambrian to Cenozoic in age.
Uses & applications
Used widely in road construction, as railway ballast, for flooring and wall coverings, and in the manufacturing of glass and ceramics. High-purity quartzite is a source of silica metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding softer rocks, forming prominent ridges or peaks. It is the hardest common rock types found in nature, even harder than the steel blade of a pocket knife.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary appearance. Unlike sandstone, when broken, quartzite fractures through the grains rather than around them. Found globally in mountainous regions.
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