metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellowish as seen here
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Often found in Precambrian and Paleozoic mountain belts.
Uses & applications
Primarily used in construction as crushed stone for road beds and railway ballast. Also used as dimension stone in architecture and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often survives intense weathering and glacial transport, explaining its presence as rounded river cobbles or glacial erratics. It is harder than steel and will scratch glass easily.
Field identification & locations
Identify by its grainy, sugary texture and extreme hardness (cannot be scratched by a steel knife). Common in riverbeds and mountainous regions. It breaks through the grains rather than around them, unlike sandstone.
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