metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, white, or tan; Luster: Vitreous to dull; Crystal Structure: Trigonal (granular texture); Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically grey, white, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, white, or tan; Luster: Vitreous to dull; Crystal Structure: Trigonal (granular texture); Cleavage: None/conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed from quartz-rich sandstone subjected to high heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic. Found in orogenic belts worldwide.
Uses & applications
Used as decorative stone in architecture, railway ballast, road construction, and occasionally in glassmaking if high purity.
Geological facts
Quartzite is so tough that it often fractures across the original grains rather than around them, which distinguishes it from sandstone under a hand lens.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its crystalline, sugary appearance. Found in mountainous or previously glaciated regions.
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