metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: White, gray, or pink/red (due to iron oxides). Luster: Vitreous to dull. Crystal structure: Trigonal (granular). Cleavage: None, breaks with a conchoidial fracture.
- Hardness
- 7 on the Mohs scale
- Color
- White, gray, or pink/red (due to iron oxides)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: White, gray, or pink/red (due to iron oxides). Luster: Vitreous to dull. Crystal structure: Trigonal (granular). Cleavage: None, breaks with a conchoidial fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). Most quartzite is hundreds of millions of years old.
Uses & applications
Used as crushed stone for road construction and railway ballast. Polished varieties are used for countertops, flooring, and decorative carvings.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary appearance. Found globally in metamorphic belts; distinctive pink varieties are common in the Baraboo Range of Wisconsin and parts of South Dakota.
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