metamorphic
Quartzite
Quartzite (predominantly SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with possible pink/red hues from iron; Luster: vitreous to waxy; Structure: granular, non-foliated; Cleavage: none, breaks with conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with possible pink/red hues from iron; Luster: vitreous to waxy; Structure: granular, non-foliated; Cleavage: none, breaks with conchoidal or irregular fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, usually in orogenic (mountain-building) belts.
Uses & applications
Used extensively in construction as crushed stone for road aggregate, as decorative dimension stone in countertops and wall cladding, and historically as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts surrounding rock in weathering processes, frequently forming the caps of ridges and mountains. It is more resistant to chemical weathering than limestone or marble.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in ancient mountain ranges like the Appalachians or the Alps. For collectors, look for sugary texture and translucent edges.
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