metamorphic
Quartzite
Quartzite (Mostly SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (pinkish-tan in this specimen); Luster: vitreous to waxy; Texture: granular, sandy, or crystalline; Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan (pinkish-tan in this specimen)
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (pinkish-tan in this specimen); Luster: vitreous to waxy; Texture: granular, sandy, or crystalline; Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, typically occurring during mountain-building events (orogeny).
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, as railroad ballast, and for manufacturing glass or silica-based products.
Geological facts
Quartzite is so tough that despite its high silica content, it is often more resistant to weathering than the surrounding rock, frequently forming ridges and hilltops in mountainous regions.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and lack of reaction to acid. It is found globally in ancient mountain belts including the Appalachian Mountains and the Scottish Highlands.
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