metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow, orange, or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal or irregular.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow, orange, or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal or irregular.
Formation & geological history
Quartzite is a non-foliated metamorphic rock that forms from the metamorphism of pure quartz sandstone. Heat and pressure cause the quartz grains to recrystallize and fuse together. It can form in various geological ages during mountain-building events (orogenies).
Uses & applications
Used extensively in construction as road ballast, flooring, and decorative wall coverings. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon. It is also used in landscaping and as a lapidary stone for bookends or jewelry.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges or hilltops. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than along the boundaries between them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its sugary, crystalline appearance. It is found globally in ancient mountain belts and shield areas. Collectors value specimens with interesting colors or embedded crystals.
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