metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Reddish-brown/pink; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Reddish-brown/pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Reddish-brown/pink; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a dense, hard rock. Often Proterozoic or Paleozoic in age.
Uses & applications
Used as decorative stone, crushed stone for road construction, railway ballast, and in some industrial manufacturing as a source of silica.
Geological facts
Quartzite is so hard and dense that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in mountain ranges or as water-worn cobbles in riverbeds and glacial deposits.
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