metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none (fractures across grains); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pink
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none (fractures across grains); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. These rocks can date back to the Proterozoic or Paleozoic eras depending on their geological setting.
Uses & applications
Used widely in construction as crushed stone for road gravel and railroad ballast, in the production of glass, for making floor tiles, and occasionally as a decorative semi-precious stone in jewelry.
Geological facts
Quartzite is so durable that it resists weathering better than most other rocks. Large outcrops often form the ridges of mountain ranges because the surrounding softer rock erodes away first.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks: unlike sandstone, which breaks around grains, quartzite breaks through them. Common in mountainous regions and glacial till.
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