metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White, grey, or tan/re; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal/irregular fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, grey, or tan/re
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, grey, or tan/re; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal/irregular fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. This typically occurs at convergent plate boundaries.
Uses & applications
Used in construction as crushed stone for road ballast, as decorative building stone, in glass manufacturing, and as high-silica raw material for industrial chemicals.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in the landscape, forming prominent ridges and hilltops. It is one of the most chemically resistant and physically durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sandpaper-like surface that lacks the visible pores of sandstone. Commonly found in mountain ranges and ancient shields like the Appalachians or the Canadian Shield.
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