metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous (glassy) to dull; Crystal structure: trigonal (hexagonal) system; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, occasionally pink or reddish
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous (glassy) to dull; Crystal structure: trigonal (hexagonal) system; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, interlocking mosaic.
Uses & applications
Used widely in road construction (as crushed stone), railway ballast, decorative countertops, flooring, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the prominent peaks and ridges of mountain ranges because it weathers more slowly than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that lacks the individual distinct grains seen in sandstone. Found worldwide in ancient mountain belts.
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