metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, pink, or reddish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, pink, or reddish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, pink, or reddish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, hard rock. It is found in mountain belts globally where tectonic activity has occurred.
Uses & applications
Used as crushed stone for road construction and railway ballast; in manufacturing glass, sandpaper, and industrial abrasives; as decorative stone for countertops, wall cladding, and flooring; and as a source of high-purity silica.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, forming prominent ridges and peaks. It is frequently confused with white marble, but can be distinguished because quartzite is harder and will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its sugary texture. Unlike sandstone, quartzite fractures across the individual quartz grains rather than around them. Common in Precambrian and Paleozoic shields.
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