metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: hexagonal (granular texture); Cleavage: none (fractures conchoidally or irregularly); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: hexagonal (granular texture); Cleavage: none (fractures conchoidally or irregularly); 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, quartz grains recrystallize and fuse together. It can be found in mountain belts and cratonic interiors across various geological ages.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, and formerly used for making stone tools (lithics). High-purity quartzite is also a source of silica for glass and silicon metal production.
Geological facts
Quartzite is so hard and durable that it often forms prominent ridges and hills because it resists weathering better than the rocks surrounding it.
Field identification & locations
Identify it by its extreme hardness (it will scratch glass and steel) and its grainy, sandpaper-like texture that does not rub off. Unlike sandstone, quartzite breaks through the grains rather than around them.
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