metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Variable, typically white, gray, reddish-pink, or brownish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6–2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Variable, typically white, gray, reddish-pink, or brownish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Variable, typically white, gray, reddish-pink, or brownish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartzose sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and roofing flakes. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass. Also used for decorative stone and countertops.
Geological facts
Quartzite is so hard that it can scratch steel. Unlike sandstone, which breaks around the individual sand grains, quartzite is so strongly fused that it breaks right through the grains when struck.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its granular, sugary appearance on fresh surfaces. Often found in mountain ranges or Shield areas where ancient sediments were compressed.
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