metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or light green; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or light green
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or light green; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. Geological age varies by location, often Proterozoic or Paleozoic.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. Fine specimens are used as decorative garden stones or aggregate.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains. It is harder than the steel of a knife, which is a key way to distinguish it from similar-appearing marble.
Field identification & locations
Identify in the field by its sugary, granular texture and extreme hardness (it will scratch glass). Common in metamorphic belts worldwide, such as the Appalachian or Rocky Mountains.
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