metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, white, pinkish-brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, white, pinkish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, white, pinkish-brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, forming a dense, interlocking matrix. This sample appears to be a river-worn or glacially rounded cobble.
Uses & applications
Used in construction as crushed stone for road gravel and railway ballast, in architecture as facing stone or flooring, and in manufacturing as a source of silica for glass and ceramics.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it is found, remaining as residual hills or 'monadnocks'. Unlike sandstone, which breaks around grains, quartzite breaks through the grains due to the strength of the silica cement.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary appearance on a fresh break. Commonly found in old mountain belts and glacial till across North America and Europe.
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