metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or yellowish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or yellowish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or yellowish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. This specimen appears water-worn, likely from a river or glacial deposit.
Uses & applications
Used as crushed stone in road construction, as railroad ballast, and for architectural facing. Some attractive pieces are used as garden stones or polished in rock tumblers.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them. It is one of the most durable and weather-resistant rocks on the Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture on fresh breaks. This specific sample's rounded shape indicates it has undergone significant transport and erosion.
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