metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray with yellowish/tannish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- white to light gray with yellowish/tannish iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray with yellowish/tannish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, creating a very hard, dense rock.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the production of glass and industrial silica. Some varieties are used as ornamental building stone.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists erosion better than the surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular appearance. Unlike sandstone, quartzite breaks through the quartz grains rather than around them.
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