metamorphic
Quartzite
Quartzite (Metamorphosed Quartz Sandstone)
Hardness: 7 on the Mohs scale; Color: Typically white to gray, but can be pink, red, or yellow due to iron oxide impurities; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Interlocking quartz crystals; Cleavage: None, breaks across quartz grains rather than around them;…
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to greasy on fractured surfaces
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Physical properties
Hardness: 7 on the Mohs scale; Color: Typically white to gray, but can be pink, red, or yellow due to iron oxide impurities; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Interlocking quartz crystals; Cleavage: None, breaks across quartz grains rather than around them; Specific gravity: 2.65 - 2.70.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically through tectonic compression in orogenic belts. The original quartz grains recrystallize along with the cementing material, fusing into a dense, extremely durable rock.
Uses & applications
Used widely in construction as crushed stone for roadbeds, railway ballast, and aggregate in concrete. Also used as dimension stone, in manufacturing refractory bricks, and occasionally as decorative stone or in landscaping.
Geological facts
Because quartz is extremely resistant to weathering and chemical action, quartzite mountains often remain as prominent ridges or peaks after surrounding softer rocks have eroded away. It is so hard that it will easily scratch glass and cannot be scratched by a steel knife.
Field identification & locations
Identified in the field by its sugary texture on broken surfaces, extreme hardness (scratches glass), and the fact that it breaks through the quartz grains rather than around them (unlike sandstone). Found worldwide in ancient mountain belts.
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