metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan or white; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: None (conchoïdal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan or white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan or white; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: None (conchoïdal 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 together. It is found in mountain-building belts worldwide.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, railroad ballast, and occasionally in glassmaking if the silica content is exceptionally high.
Geological facts
Quartzite is so strong that when it breaks, the fracture passes through the quartz grains themselves rather than around them, which distinguishes it from sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its granular, sugary texture. Common in eroded mountain ranges. Can be confused with marble but will not react to acid.
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