metamorphic
Quartzite
Quartzite (composed primarily of Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Pink, reddish, tan, or gray due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Pink, reddish, tan, or gray due to iron oxide impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, reddish, tan, or gray due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, typically during mountain-building events (orogeny). The quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used as a decorative stone in construction, road ballast, kitchen countertops, and as a source of silica in glassmaking and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and peaks. It is harder than glass and cannot be scratched by a steel knife.
Field identification & locations
Identify by its extreme hardness and grainy texture that, unlike sandstone, breaks across the grains rather than around them. Common in mountainous regions like the Appalachians or the Rockies.
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