metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or tan (buff); Luster: Vitreous to dull; Texture: Granular, crystalline (sugar-like fracture); Cleavage: None (conchoidal to irregular fracture).
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or tan (buff)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or tan (buff); Luster: Vitreous to dull; Texture: Granular, crystalline (sugar-like fracture); Cleavage: None (conchoidal to irregular fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, hard rock. It is found in mountain belts and Precambrian shields worldwide.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative stone in architecture (countertops, flooring); and as a source of silica for glass making and metallurgy.
Geological facts
Quartzite is so hard and durable that it often forms the crests of ridges and mountain peaks because it resists weathering better than surrounding rocks. It is distinct from sandstone because it breaks across the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (will easily scratch glass) and its 'sugary' appearance on freshly broken surfaces. Common in Appalachian Mountains, Lake Superior region, and Brazil. Collectors look for unique colors caused by mineral inclusions like iron or fuchsite.
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