metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan with brown staining; Luster: Dull/earthy on surface, vitreous when broken; Crystal Structure: Granular/Massive; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan with brown staining
- Luster
- Dull/earthy on surface, vitreous when broken
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan with brown staining; Luster: Dull/earthy on surface, vitreous when broken; Crystal Structure: Granular/Massive; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together. Most deposits date back to the Proterozoic or Paleozoic eras.
Uses & applications
Commonly used as crushed stone in road construction, as railroad ballast, and occasionally for decorative landscaping or historical toolmaking (debitage).
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Look for a sugary, granular texture and extreme hardness (will scratch glass). Commonly found in riverbeds as rounded cobbles due to high resistance to erosion.
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