metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish/tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellowish/tan due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish/tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard mass.
Uses & applications
Used as crushed stone in road construction, as a decorative stone in landscaping and flooring, and occasionally as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It is one of the most durable rocks found on the Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and the way it breaks through the quartz grains rather than around them. Common in mountainous regions like the Appalachians or the Alps.
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