metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be brownish as seen here; Luster: vitreous or dull; Crystal structure: non-foliated, granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, but can be brownish as seen here
- Luster
- vitreous or dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be brownish as seen here; Luster: vitreous or dull; Crystal structure: non-foliated, granular; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, usually during mountain-building events (orogenic periods).
Uses & applications
Used widely in road construction (crushed stone), as architectural stone for flooring and countertops, and in high-purity forms for silica glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks, forming resistant ridges and hilltops. It is one of the hardest commonly occurring rocks in the Earth's crust.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel blade) and its tendency to break through the sand grains rather than around them. Found globally in ancient shield areas and mountain ranges like the Appalachians or the Alps.
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