metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale. Color: Typically white to gray, but can be pink, red, or brown due to iron oxide impurities. Luster: Vitreous to greasy on fractured surfaces. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None (fractures conchoidally through grains).…
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to greasy on fractured surfaces
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Physical properties
Hardness: 7 on Mohs scale. Color: Typically white to gray, but can be pink, red, or brown due to iron oxide impurities. Luster: Vitreous to greasy on fractured surfaces. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None (fractures conchoidally through grains). Specific gravity: 2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, usually through tectonic compression during mountain building (orogenesis). The original quartz grains recrystallize and fuse tightly together with silica cement.
Uses & applications
Used in construction, as crushed stone for roadbeds, railway ballast, dimension stone, and in the production of silica refractory bricks and ferrosilicon.
Geological facts
Unlike sandstone, which breaks around the individual sand grains, quartzite breaks straight through the grains because the interlocking quartz crystals are so strongly bonded.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily, cannot be scratched by a steel knife), lack of reaction to acid, and sugary, interlocking crystalline texture on broken faces.
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