metamorphic
Quartzite
Quartzite
Hardness: 7 (Mohs scale); Color: Reddish-brown, gray, or white; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Reddish-brown, gray, or white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Reddish-brown, gray, or white; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. Often associated with Precambrian or Paleozoic mountain building events.
Uses & applications
Used in construction as ballast for railways, as a decorative stone in landscaping, for floor tiles, and historically as a prehistoric material for stone tools.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges because it resists erosion much better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its grainy, crystalline texture that breaks through the grains, not around them. Very common in old metamorphic shields like those in Canada, Scandinavia, and the US Midwest.
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