metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (harder than glass); Color: White, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal system in fine grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale (harder than glass)
- Color
- White, gray, or tan with a sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass); Color: White, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal system in fine grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. Can range from Precambrian to relatively recent geological eras.
Uses & applications
Used extensively in construction as road ballast, railway ballast, and crushed stone. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon for the electronics and steel industries.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, forming prominent ridges and hilltops. It is frequently mistaken for marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch a steel knife or glass) and its 'sugary' crystalline appearance on a fresh break. Commonly found in mountain ranges and ancient metamorphic shields globally.
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