metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Hexagonal/trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown to tan (due to iron oxide)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Hexagonal/trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into a dense interlocking mosaic.
Uses & applications
Used in construction as a decorative stone, railway ballast, and crushed stone for roadbeds. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so durable that it often remains as mountain peaks or ridges after the surrounding softer rocks have eroded away. It is significantly harder and more resistant than the sandstone from which it originates.
Field identification & locations
Identify in the field by its hardness (it should scratch glass easily) and its sugary texture where broken. Unlike sandstone, when quartzite breaks, the fracture goes through the quartz grains rather than around them.
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