metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown (due to iron oxide impurities), purple, or grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
Identified More metamorphic →
Explore Quartzite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown (due to iron oxide impurities), purple, or grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. This typically occurs during tectonic mountain-building events.
Uses & applications
Used in construction as crushed stone for road grit, railroad ballast, and flooring. Due to its hardness, it is also used as an abrasive and in the glass-making industry.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains themselves rather than around the boundaries between them, unlike its parent rock, sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that does not rub off. Commonly found in folded mountain belts and glacial till.
More like this
