metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (as quartz); cleavage: none, has a sugary conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (as quartz); cleavage: none, has a sugary conchoidal fracture.
Formation & geological history
Quartzite is formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, hard rock. This process often occurs during mountain-building events (orogeny).
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. In industry, high-purity quartzite is a source of silica for glass and silicon metal production. It is also used as decorative stone in landscaping.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is more resistant to weathering than the surrounding rock, which is why it often forms the crests of ridges and resistant hilltops.
Field identification & locations
Identify in the field by its extreme hardness and its tendency to break across quartz grains rather than around them, giving it a grainy, sugary appearance on fresh surfaces. It is found in ancient mountain belts worldwide.
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