metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or tan; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing quartz grains to recrystallize and fuse together into a dense, hard masonry.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop material. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and the way it breaks through the sand grains rather than around them, unlike sandstone. Widely found in mountain ranges.
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