metamorphic
Quartzite
Quartzite (consisting primarily of SiO2)
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks across grains); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pink, reddish-brown, or tan due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks across grains); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together. Most common in Precambrian and Paleozoic rock units.
Uses & applications
Used in construction as crushed stone for road grit and railroad ballast. Frequently used as decorative stone in landscaping and occasionally in lapidary work for cabochons.
Geological facts
Quartzite is so durable that it often survives erosion better than the surrounding rocks, frequently forming the tops of ridges and mountains. It is harder than steel and can easily scratch a glass bottle.
Field identification & locations
Identify in the field by its sugary texture and inability to be scratched by a steel knife. It will break through the quartz grains rather than around them, unlike sandstone. Common in mountainous regions and glacial drift.
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