metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. Typically found in mountain belts (orogenic zones).
Uses & applications
Used in construction as crushed stone or dimensional stone, for railroad ballast, and sometimes in the manufacturing of glass or as a decorative landscaping stone.
Geological facts
Quartzite is so durable that it often outlasts the surrounding rocks during erosion, forming ridges and resistant outcrops. It is often confused with marble, but unlike marble, it will not fizz in contact with acid.
Field identification & locations
Identify by its extreme hardness (it will scratch glass) and its sugary, granular texture. It breaks across quartz grains rather than around them. Commonly found in areas with ancient mountain ranges or in glacial deposits.
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