metamorphic
Quartzite
Quartzite (Mostly SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish-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
- Tan, brown, or grayish-tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish-tan; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic.
Uses & applications
Used in construction as road ballast, railway ballast, and decorative stone. Sometimes used in glassmaking or as a source of silica in industry.
Geological facts
Quartzite is so durable that it often forms the tops of ridges and mountains because it resists weathering better than the surrounding rock types.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. Commonly found in folded mountain belts and ancient cratons.
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