metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan to light brown (due to iron oxides); Luster: Vitreous to sugary; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan to light brown (due to iron oxides)
- Luster
- Vitreous to sugary
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan to light brown (due to iron oxides); Luster: Vitreous to sugary; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together into a dense, hard rock. Various geological ages from Precambrian to Cenozoic.
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and building stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass. Also popular for landscaping and as decorative 'river rock'.
Geological facts
Quartzite is so hard that it will scratch glass and steel. Unlike sandstone, which breaks around the sand grains, quartzite breaks through the grains themselves because it is so well-cemented.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife) and its grainy, sugary texture. It is commonly found in fold mountain belts globally. It is more resistant to weathering than most other rocks, often forming ridges or hilltops.
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