metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with reddish tints from iron; Luster: vitreous to dull; Crystal structure: hexagonal crypto-crystalline; Cleavage: none, breaks with conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan with reddish tints from iron
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with reddish tints from iron; Luster: vitreous to dull; Crystal structure: hexagonal crypto-crystalline; Cleavage: none, breaks with conchoidal fracture.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (regional metamorphism), causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming prominent ridges or hilltop caps. It is one of the most physically durable and chemically resistant rocks found on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks through quartz grains rather than around them. Commonly found in folded mountain belts and ancient shield areas.
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