metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with reddish tints from iron; Luster: vitreous to glassy; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal or irregular fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan with reddish tints from iron
- Luster
- vitreous to glassy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with reddish tints from iron; Luster: vitreous to glassy; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal or irregular fracture).
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating a dense, interlocking matrix. Found in mountain belts and Precambrian shields.
Uses & applications
Used widely in construction as crushed stone for road gravel and railway ballast, as dimension stone for wall cladding and flooring, and occasionally as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. Because it is composed of quartz, it will scratch glass easily, distinguishining it from similar-looking marble.
Field identification & locations
Identify in the field by its grainy appearance (reminiscent of sandpaper but smooth to the touch) and its extreme hardness. It won't react with acid, unlike carbonate rocks. Common in the Appalachian Mountains and the Great Lakes region of North America.
