metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (sometimes pink or yellow due to impurities); Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; 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 (sometimes pink or yellow due to impurities); Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together, creating a hard, interlocking network.
Uses & applications
Used widely in construction as crushed stone for roadbeds and railway ballast. High-purity quartzite is used to produce silica sand for glassmaking. Also used as a decorative stone in architecture and landscaping.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently capping hills and mountain ridges. Unlike sandstone, which breaks around grains, quartzite breaks through them because the cement is as strong as the grains.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch steel) and its crystalline, sugary appearance on fresh breaks. It is commonly found in ancient mountain belts and riverbeds as rounded cobbles like this specimen.
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