metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to grey (pure), pink/red/yellow (impurities); Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to grey (pure), pink/red/yellow (impurities)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey (pure), pink/red/yellow (impurities); Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). Generally found in old continental shields and fold belts.
Uses & applications
Used in construction as crushed stone for road bases and railway ballast, as a decorative stone in architecture (countertops, tiles), and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its ability to scratch glass and lack of reaction with HCl (unlike marble). Look for a sugary, granular texture where individual quartz grains have fused together. Common in the Appalachian Mountains and the Alps.
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