metamorphic
Quartzite
Quartzite (SiO2 silicon dioxide)
Hardness: 7 (Mohs scale); Color: White to grey, sometimes yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (often appears granular); Cleavage: Indistinct; Specific gravity: 2.6-2.7. It is extremely durable and hard.
- Hardness
- 7 (Mohs scale)
- Color
- White to grey, sometimes yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to grey, sometimes yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (often appears granular); Cleavage: Indistinct; Specific gravity: 2.6-2.7. It is extremely durable and hard.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism). This process fuses the individual quartz grains into a solid mass of interlocking quartz crystals. It can range in age from Precambrian to more recent tectonic events.
Uses & applications
Used in construction for road ballast and railway track ballast, as dimension stone for flooring and walls, and crushed for glass manufacturing and industrial abrasives. High-purity quartzite is a source of silicon.
Geological facts
Unlike sandstone, which breaks around grains, quartzite breaks through the grains due to its recrystallized structure. It is often resistant to chemical weathering and creates prominent ridges in mountain ranges.
Field identification & locations
Identify by its excessive hardness (will easily scratch glass or steel) and sugary, granular texture. It is commonly found in fold mountain belts globally. Unlike calcite-based rocks, it will not fizz with acid.
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