metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, pink, or yellowish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, gray, pink, or yellowish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, pink, or yellowish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); 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 quartz grains to recrystallize and fuse together. These often date back to the Proterozoic or Paleozoic eras.
Uses & applications
Used in construction as crushed stone for road gravel and railway ballast, in architecture as decorative stone or countertops, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges and peaks in mountain ranges. It is harder than the steel of a knife blade.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass) and its sugary, granular surface that looks like sandpaper but feels smooth. Unlike marble, it does not fizz when exposed to acid. Commonly found in folded mountain belts.
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