metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, sometimes yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to grey, sometimes yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey, sometimes yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can date from almost any geological era where sandstone was present.
Uses & applications
Used as crushed stone for road construction and railway ballast. Due to its durability, it is used for floor tiles, countertops, and decorative wall coverings. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often breaks through the internal quartz grains rather than along their boundaries, unlike its parent sandstone. It is resistant to chemical weathering and creates prominent ridges in mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary or grainy texture that looks like sandpaper but feels smooth to the touch. It is found worldwide in mountain belts like the Appalachians or the Alps.
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