metamorphic
Quartzite
Metamorphic rock primarily composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.63 - 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white with iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.63 - 2.65
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard mass of interlocking quartz crystals.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone and for floor tiles.
Geological facts
Quartzite is so hard that it can easily scratch glass and stainless steel. It is more resistant to weathering than the sandstone it originated from, often forming the caps of ridges and hills. Some ancient people used it to create stone tools because of its conchoidal fracture pattern.
Field identification & locations
Identify by its extreme hardness and grainy, sugary texture on fresh surfaces. Unlike sandstone, quartzite breaks through the sand grains rather than around them. Found globally in mountainous regions and ancient shield areas.
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