metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White to grayish-white; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to grayish-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to grayish-white; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking matrix. Found in orogenic belts worldwide, often dating from the Precambrian to Cenozoic eras.
Uses & applications
Used extensively in construction as road ballast, roofing granules, and dimension stone. High-purity quartzite is used in the manufacture of glass, silicon metal, and ferrosilicon. It is also a popular material for kitchen countertops and decorative landscaping.
Geological facts
Quartzite is so tough that it often outlasts the rocks around it, forming prominent ridges and mountaintops. It is frequently mistaken for marble, but can be easily distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, crystalline texture upon a fresh break. Unlike sandstone, quartzite breaks through the sand grains rather than around them. Found globally in mountainous regions like the Appalachians, Alps, and Urals.
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